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YAG (Y3Al5O12) transparent ceramics have attractive application prospects for transparent armor protection modules because of their excellent light transmittance and anti-ballistic capability. Understanding the fracture behavior and damage mechanism of YAG is necessary for armor design. To explore the damage characteristics of YAG under compression and tension, shock compression and shockless spalling experiments with soft recovery technique are conducted. The spall strength of YAG is obtained and the recovered samples are observed by CT and SEM. It is shown that the macroscopic damage characteristic of YAG under compression is vertical split cracks with oblique fine cracks distributed in the entire sample, while that under tension is horizontal transgranular cracks concentrated near the main spall surface. The cracks generated by macroscopic compression, tension and shear stress extend in similar tensile form at the microscale. The proportion of transgranular fractures on spall surfaces is higher than that of cracks induced by macroscopic compression. Meanwhile, higher loading rate and longer loading duration increase the transgranular fracture percentage.

Sintering additives and micro-powder injection molding offer an effective method to densify boron carbide (B4C) and make B4C components with complex shapes. By adjusting the proportion of three kinds of powders (SiC, Al2O3 and Y2O3), four kinds of sintering additives were prepared. The feedstock uniformity, debinding behavior, phase composition and microstructure of micro injection molded B4C components with different sintering additives were studied. The results showed that the defects such as lattice distortion and vacancy were introduced into ball milling, which increase the surface energy and benefit subsequent sintering densification. The feedstock had good uniformity and rheology that met the requirements of micro powder injection molding. After debinding, B4C components had enough strength and showed certain sintering characteristics. The addition of sintering additives was beneficial to densification and sintering temperature reduction. The addition of sintering additives formed a second phase in the B4C crystal and at the grain boundary of B4C crystal, which changed the fracture mode from transgranular fracture to mixed fracture mechanism with transgranular fracture.

The effect of deformation temperature on tensile behavior of Inconel 718 alloy has been studied by a self-developed in-situ high-temperature tensile stage inside a scanning electron microscopy at a temperature range from room temperature (RT) to 750 °C. The dynamic microstructure evolution and mechanical properties at different temperatures were performed and compared by the uniaxial tensile tests. The in-situ test results showed that the mechanical properties and fracture mechanisms of Inconel 718 alloy were sensitive to deformation temperatures. From RT to 650 °C, the yield stress and ultimate tensile strength decrease slightly and the tensile ductility is comparable. While up to 750 °C, the yield stress and ultimate tensile strength decrease significantly, the elongation and reduction of cross section also showed a significant decrease from RT to 750 °C. It was found that at RT and 650 °C, tensile cracks tended to initiate around the carbide particles and the triple junctions of grain boundaries, also propagated transgranularly; at 750 °C, the cracks initiated at grain boundaries and propagated intergranularly. In fact, with the increase in deformation temperature, the fracture mechanism transformed from the ductile transgranular fracture to the brittle intergranular fracture.

The purpose of this paper was to study the failure behavior of SUS304 stainless steel in view of cooling water leakage in actual service conditions. The temperature field and thermal stress distribution in the thickness direction of SUS304 stainless steel under actual service conditions were further analyzed by the finite element method. The results show that chromium-rich carbides are precipitated at the grain boundaries, which may cause intergranular corrosion. The morphology of the corrosion grooves is ditch structure, which has high intergranular corrosion susceptibility. The expansion direction of the cracks is from the contact surface of cooling water to the high-temperature contact surface. Fracture is characterized by a river pattern and rock candy pattern. Fracture morphology is characterized by brittle rupture. The Cl contained in the corrosion products comes from the circulating cooling water. XRD patterns show that the corrosion products are composed of CaCO3 (the high-temperature contact surface) and Fe3O4 (the contact surface of cooling water), respectively. EDS results of corrosion products are consistent with XRD results. The results of finite element simulation show that the temperature field along the thickness direction of SUS304 stainless steel plate is in the range of 436.6-450 °C. The peak of thermal stress is located in the middle of cross section. The cause of failure is acceleration of the initiation and extension of the cracks under the combined action of chloride ion stress corrosion, intergranular corrosion, and thermal stress. The form of crack fracture is mixture of transgranular and intergranular fracture, mainly transgranular fracture, which belongs to typical chloride ion stress corrosion.

This paper examines the influence of 0-0.2 wt.%B-doping on the microstructure, mechanical properties, and pseudoelastic behavior of Cu-Al11.5-Be0.57 shape memory alloys (SMAs). This microstructure study reveals that the addition of boron leads to significant grain refinement in $$\beta_{1}$$ -type polycrystalline Cu-Al-Be SMAs. A maximum refinement size of 50 µm was achieved with the addition of 0.15 wt.%B. The fine-grained (Cu-Al11.5-Be0.57)-B0.15 SMA with serrated grain boundaries exhibited the maximum enhancement of ultimate tensile strength, 744.65 ± 29.34 MPa, and ductility of 21.93 ± 0.56%. The fracture morphology revealed the transformation of intergranular to transgranular fracture in the SMAs with boron-doping. Maximum pseudoelasticity of 4% was achieved in the SMA with 0.15 wt.%B and suits as a damper in seismic applications.

High entropy alloy (HEA) of FeCoNiTiAl and Inconel 718 superalloy were firstly transient liquid phase (TLP) bonded by BNi2 filler due to the diffusion of Si and B in the filler to the base metals. The effects of bonding time on microstructure evolution and mechanical properties of the TLP joints were investigated. Owing to the complete isothermal solidification of the joints bonded for 30 min ∼ 120 min at 1100 °C, no athermally solidified zones (ASZs) formed by eutectic phases were observed in the welded zone. Thus the TLP joints were only composed by the isothermally solidified zone (ISZ) and two diffusion affected zone (DAZ) adjacent to the dissimilar base metals and the negative effect of the ASZ on joint properties can be avoided. In addition, the increase of the bonding time can also make the TiB2 borides precipitated in the DAZ near HEA and the brittle borides or carbides in the DAZ near IN718 alloy decrease and reduce the possibility of the stress concentration happened in the joints under loading. Therefore, the highest shear strength (632.1 MPa) of the TLP joints was obtained at 1100 °C for 120 min, which was higher than that of the joint bonded for 30 min, 404.2 MPa. Furthermore, the extension of the bonding time made the fracture mechanism of the joint be transformed from the intergranular fracture to the transgranular fracture. However, as the brittle borides in the DAZ near IN718 can not be eliminated completely and refining of grains also happened in such region, all the TLP joints fractured inner the DAZ near IN718 alloy.

The environment at crack tip and its effect on the crack growth behaviour of low alloy steel-E690 steel were studied at cathodic potentials in artificial seawater. The results showed that the micro environment at crack tip and crack growth behaviour were related to the electrochemical reactions at crack tip, which were affected by the stress state and applied potentials. The crack tip environment was acidified under cyclic loading, resulting from the crack tip anodic dissolution reaction and corresponding hydrolysis reaction. Because of the hydrogen evolution and the inhibited anodic dissolution inside the crack, the crack tip p H increases as the cathodic potential decreases. The effect of cathodic potentials on the electrochemical reactions caused the variation of the hydrogen content, which influenced the crack growth rate because the crack growth behaviour was controlled by hydrogen embrittlement mechanism. This resulted in a fact that with the negative decrease of potential, the crack growth rate first decreased and then increased,with the minimum rate at-0.75 V. And the crack growth path exhibited transgranular fracture.

In this paper, the mechanical properties and microstructures of an Al-Zn-Mg-Cu alloy subject to two-step aging treatment were systematically investigated. The results indicate that the mechanical strength and tensile ductility of the alloy can be significantly improved by pre-aging treatment at 120 °C for 6 h and then by second-step aging treatment at 165 °C for 12 h. After second-step aging treatment at 165 °C for 12 h, the tensile strength and yield strength of the alloy reach 718 and 654 MPa, increased by ~ 23 and ~ 35%, respectively, compared to the alloy without aging treatment. The increment in the strength is mainly attributed to the formation of ultrafine metastable η′ phase dispersed in the matrix. The fracture mode of the aging treated alloy includes both intergranular fracture and dimpled transgranular fracture. The coarse grain boundary precipitates (MgZn2 phase) and the wide precipitation free zones are beneficial to the tensile ductility of the alloy.

In this study, high-speed milling of marble was conducted with a coated carbide ball nose end mill. Single-factor cutting tests were designed to investigate the effect of milling parameters on cutting forces and marble chips. It was found that the cutting forces in three directions increased with the increasing feed rate and decreased with the increasing cutting speed. The morphology and particle size of marble chips were analyzed. The transgranular fracture was found to be the predominant failure mode in the milling process. In addition, it was found that the particle size of marble chips increased with the increasing feed rate and decreased with the increasing cutting speed. There was an obvious positive correlation between the cutting forces and chip formation. The experimental results were significant for a better understanding of the material removal mechanism and selection of cutting parameters in the machining of rock materials.

The effects of tritium on the fracture toughness properties of Type 304L and Type 21-6-9 stainless steel weldments were measured. Weldments were tritium-charged-and-aged and then tested in order to measure the effect of the increasing decay helium content on toughness. The results were compared to uncharged and hydrogen-charged samples. For unexposed weldments having 8-12 volume percent retained delta ferrite, fracture toughness was higher than base metal toughness. At higher levels of weld ferrite, the fracture toughness decreased to values below that of the base metal. Hydrogen-charged and tritium-charged weldments had lower toughness values than similarly charged base metals and toughness decreased further with increasing weld ferrite content. The effect of decay helium content was inconclusive because of tritium off-gassing losses during handling, storage and testing. Fracture modes were dominated by the dimpled rupture process in unexposed weldments. In hydrogen and tritium-exposed weldments, the fracture modes depended on the weld ferrite content. At high ferrite contents, hydrogen-induced transgranular fracture of the weld ferrite phase was observed.

Excellent comprehensive mechanical properties including good formability, high strength and high ductility are prior demands for Al-Mg-Si-Cu alloys. This study utilizes calculation of phase diagram (CALPHAD) to simplify the alloy design and meet these demands. Specifically, CALPHAD was used to finely tune the Mg/Si atomic ratio in solid solution and accurately control the type and content of second phases, especially to avoid the formation of the harmful constituent phase β-AlFeSi. Constituents and dispersoids of only α-AlFeMnSi phase were found in the alloy prepared. An optimized microstructure with fine grains, micro scale constituents, densely distributed submicron scale dispersoids and extremely dense nano precipitates provides effective impediment to dislocation gliding and induces transgranular fracture. Therefore, the designed alloy has better comprehensive mechanical properties than other 6xxx series aluminum alloys, including excellent formability, strength and ductility. The low T4P strength of 149 MPa as well as the high elongation of 26.1% implies the alloy's applicability to automobile body panel forming. The yield strength was rapidly improved from 149 MPa to 277 MPa during the paint bake ageing, because the number density of precipitates is twice as high as that of some other 6xxx alloys. Meanwhile, the elongation was kept at a high level of 20.0%.

The ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheets with the thickness of 0.06–0.15 mm were prepared from the secondary recrystallized sheets via rolling. The recrystallization texture evolution, magnetostriction and mechanical properties in the rolled sheets during the annealing at 1200 °C for 1.5–3 h were investigated. Results indicated that the magnetostriction of the ultra-thin sheet was closely related to the texture evolution depended on heat-treatment process. The major textures in the as-rolled sheet were {113} and {111} deformed texture, and the saturation magnetostriction was only ~ 63 ppm. However, an ideal {100} texture was obtained in the recrystallized sheets annealed at 1200 °C for 2 h, producing a corresponding magnetostriction of 147 ppm. Based on texture analysis, the appearance of cubic texture is mainly the consequence of the existence of cubic nuclei and transitional orientation {113} in deformed grains as well as the lowest surface energy at the (100) plane. Compared with Goss secondary recrystallized (Fe83Ga17)99.9(NbC)0.1 sheet with a thickness of 0.3 mm, the tensile ductility of cubic recrystallized ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheet was obviously improved from 2.4 to 4.4%, which was mainly attributed to the primary recrystallized microstructure with small grain size and transgranular fracture mode. The ultra-thin cubic textured (Fe83Ga17)99.9(NbC)0.1 sheets could significantly reduce eddy current losses at high frequency, and meet the requirements of low eddy current loss and high toughness for specific applications, such as ultrasonic applications and torque sensors.

A new lightweight magnesia refractory for working linings of high-temperature furnaces was prepared by using microporous magnesia aggregates instead of conventional dense magnesia aggregates. The median pore size of the microporous magnesia aggregates was 2.97 μm, while the apparent porosities of the microporous and dense aggregates were 33.3% and 5.5%, respectively. The phase composition, microstructures, fracture behaviors and strengths at room and high temperature of the lightweight magnesia refractory in comparison with those of the dense one were measured by means of XRD, SEM and three-point bending instrument. After the dense aggregates were replaced by the microporous ones, a better aggregate/matrix interface bonding was observed and the fracture mode changed from intergranular to transgranular fracture, which significantly improved the mechanical properties. Thus, the lightweight magnesia refractories had a lower bulk density of 11.8%, a higher apparent porosity of 56.2% as well as a higher flexural strength at room and high temperature of 48.4% and 160.0% comparing with the dense one, respectively.

Purpose This paper aims to evaluate the influence of molybdenum disulfide (MoS2) concentrations (5, 7.5, 10, 12.5 and 15 Wt.%) on the microstructure and tribological property of the self-lubrication cubic boron nitride (CBN) abrasive composites. Design/methodology/approach Three point bending method and rotating sliding test are used to evaluate the flexural strength and tribological property of self-lubricating CBN abrasive composites. Microstructure, wear morphology of the ball and scratch are supported by scanning electron microscopy, optical microscope and three-dimensional confocal microscopy, etc. Findings The MoS2 concentration has a significant influence on the interface microstructure between CBN abrasives and matrix alloys, and thus, affects the flexural strength of CBN abrasive composites. The grain fracture modes of CBN abrasive composites are transformed from the transgranular fracture into intergranular fracture as the MoS2 concentrations increase. Additionally, the friction coefficient of as-sintered samples decreases with the MoS2 concentrations. The MoS2 concentrations of 10 Wt.% are final determined to fabricate self-lubricating composites in basis of the mechanical and lubricating property. Originality/value The ball is fabricated under vacuum sintering process. The tribological property of self-lubricating CBN abrasive composites is evaluated in terms of the friction coefficient and morphologies of the ball and scratches after rotating sliding tests.

The present paper is related to the conversion of Ti-6Al-4V chips into powder and investigates the usability of the produced powder in powder metallurgy applications. In this regard, a disc-milling process was applied to Ti-6Al-4V chips and the obtained powder was subsequently compacted. The compacted samples were sintered by the sinter hot isostatic pressing (sinter-HIP) method at 1200°C under high vacuum, their mechanical properties and microstructure were investigated and compared with those of commercial powder compacts subjected to the same preparation processes. The results showed that the produced powder exhibits greater flowability and higher apparent density than the commercial powder. However, the sintered products prepared from the commercial powder exhibited a higher relative density, lower porosity, and, as a result, greater flexural strength compared with the sintered compacts prepared from the produced powder. In addition, transgranular fracture was greater in the sintered products of the commercial powder. The microstructural studies revealed that the sintered products made from both the commercial and the produced powders consisted of α- and β-phase but contained more α-phase. All of the examined properties were found to be substantially affected by the particle size of the powders.

An Al-8Mg-based alloy with high strength and high ductility was developed by adding a grain boundary strengthening element. Zr was predicted to be the most effective element for grain boundary strengthening at 298 K from first-principles calculations. Then, an Al-8Mg-0.2Zr alloy was developed. Grain boundary analysis by high-angle annular dark-field scanning transmission electron microscopy and Auger electron spectroscopy revealed that the added Zr segregated at grain boundaries in the Al-8Mg-0.2Zr alloy. The Al-8Mg-0.2Zr alloy exhibited tensile elongation of 49% with transgranular fracture, whereas the Al-8Mg alloy exhibited tensile elongation of 28% with intergranular fracture after tensile tests at room temperature. We succeeded in developing a high strength and high ductility Al-8Mg-0.2Zr alloy which compensates for the trade-off between strength and ductility in comparison with commercial Al alloys.

The use of Al-Mg-Si-Mn alloys is increasing in the transportation sector. This study examines the role of Mn additions (alloys with 0.02 and 0.5 wt.% Mn) on the microstructure and mechanical behaviour for two different cooling paths after solution treatment, i.e. quenching in ice water and then artificial ageing at 180 °C to the peak strength or directly quenching into an oil bath at 180 °C. The grain structure and crystallographic texture were characterized by EBSD while the precipitate state was quantified by TEM, both within in the grain and at grain boundaries. The mechanical response was examined by uniaxial tensile tests where the stress strain response was measured up to the fracture point by measuring the fracture area. It is was found that the addition of Mn increased quench sensitivity, primarily due to precipitation of Mg2Si on the Mn rich dispersoids, but the strain to fracture was approximately doubled. A precipitation hardening model which accounted for the strength loss due to precipitation on grain boundaries and dispersoids was developed and found to give good agreement with the experimental yield stress results. The role of Mn rich dispersoids on the distribution of slip and the resulting final failure mechanism was examined (i.e. transgranular vs. Intergranular). It was observed that Mn dispersoids homogenize the slip process and promote a transgranular fracture mode.

In order to understand the high-temperature deformation behavior of a nickel-based superalloy, a range of tensile tests were carried out at 720, 750, and 780 °C with strain rates ranging from 5 × 10−5 to 5 × 10−3 s−1. A piecewise constitutive model was applied to describe the work hardening-dynamic recovery and dynamic flow softening behaviors. The predicted flow stresses have a good agreement with the experimental results. Microstructures in the fracture frontier of the ruptured specimens were analyzed to further understand the fracture mechanism. Twinning and dislocation structures were surveyed at the tested conditions. Twin structure decreased as temperature increased. These two precipitates were characterized: M23C6 carbide located in the grain boundary and spherical γ′ phase in the matrix. Precipitates, twin and dislocation structures are the dominant strengthening mechanism of the superalloy during high-temperature deformation. Orientations //RD and //RD were detected as the main texture structure. Cavities formed near the precipitates and triple grain boundary. On the basis of fracture surface observations, the 750H superalloy shows both intergranular and transgranular fracture mode in the tested conditions. The dimples became small and shallow as the strain rate increased.

The aim of this study is to report the impact of microstructure on the tensile and fatigue properties of laser-welded DP780 and DP980 high-strength steel joints. The grain size at the fusion zone of the DP780/DP980 welded joint (WJ) was larger, but the microstructures at the sub-critical zone, inter-critical zone, fine-grained zone and coarse-grained zone at the DP780 and DP980 sides of DP780/DP980 WJ were not significantly different from those of DP780/DP780 WJ and DP980/DP980 WJ, respectively. The evolution trend of microhardness for the three types of WJs was consistent, featuring valleys in the softening zone and peaks in the hardening zone. The yield strength of DP780/DP980 WJ was 1.15 and 1.17 times greater than that of DP780/DP780 WJ and DP780 BM, respectively. The elongation of DP780/DP980 WJ was 6.49%, lower than the 9.22% of DP780/DP780 WJ but closer to the 6.19% of DP980/DP980 WJ. The yield-to-tensile ratio of DP780/DP980 WJ was 1.15 times that of DP780/DP780 WJ and 92.9% of DP980/DP980 WJ. The fatigue strength of DP780/DP980 WJ was 1.36 times that of DP780/DP780 WJ and 80.9% of DP980/DP980 WJ. The fatigue cracks of DP780 BM and DP980 BM propagated along the two-phase interface or inside the ferrite, and the secondary crack mainly occurred at the martensite and ferrite junction. However, the main fatigue cracks for all the WJs showed noticeable transgranular fracture, and the origin of the secondary crack was located at the grain boundary or inner grain. Fatigue crack initiations for all samples were located at the surface. The fatigue crack initiations for DP780 and DP980 BMs were mainly caused by the dislocation movement hindered by the harder martensite and impurities in the samples, while, the fatigue crack initiations of all the WJs were mainly due to oxide inclusions on the fusion zone surface.

Modeling of crack deflection/penetration or manifested as intergranular/transgranular fracture in polycrystals has long been a challenge in both fracture mechanics and materials science. A phase-field model formulated with two-set order parameters describing the crack field and the microstructure field respectively, is herein established to investigate the competition between crack penetration and deflection at an interface. The advantages of the proposed model are three-fold: (1) the fracture toughness of grain boundaries and/or interfaces, besides single crystal properties (e.g., Young’s modulus, Poisson ratio, and fracture toughness), can be automatically incorporated, (2) cohesive interfaces are treated in one phase-field framework in comparison with the integrated phase-field and cohesive zone model in which cohesive elements have to be manually placed at the interface, and (3) two-set order parameters enable to describe the concurrent crack propagation and microstructure evolution. The proposed model is validated by comparing the simulated critical deflection angles with the results from theoretical analysis of the linear elastic fracture mechanics and the experiments. The model is then applied to a heterogeneous Silicon Nitride polycrystal to determine the effect of interface fracture toughness on the intergranular/transgranular fracture transition and the effective toughness of the materials.

Melt growth Al2O3–ZrO2 eutectic ceramic has excellent high-temperature strength, creep resistance, oxidation resistance and ultra-high-temperature microstructural stability, which is expected to become one of the ideal high-temperature structural materials. Directed laser deposition (DLD) is a new technology for fabrication of melt growth eutectic ceramics, which can rapidly fabricate net-shaped ceramics. Aiming at decreasing crack and pore defects in samples prepared by DLD, different proportions of SiC particles (SiCp) are doped into Al2O3–ZrO2. Results show that SiCp distributes uniformly in Al2O3–ZrO2 eutectic ceramic matrix. Interfacial reaction occurs between SiCp and matrix. Two kinds of white phases rich in C, Si, Zr elements are formed around SiCp, and they are closely bonded with SiCp and matrix. The number and the maximum length of cracks in sample decrease obviously with the addition of SiCp. When the content of SiCp increases from 0 to 25 wt%, the number of cracks decreases 93% and the maximum cracks length decreases 92%. Some energy dissipation mechanisms such as crack pinning, transgranular fracture, crack deflection and bifurcation have remarkable effect on crack suppression. In addition, SiCp plays a significant role in eliminating pores, which reduces the porosity from 11.71 to 0.20%. Doping SiCp can increase the temperature and enhance the convection and disturbance of melt pool. Also, it can provide discharge channels for bubbles in melt pool.

The monolithic Ti5Si3 was synthesized by mechanically activated self-propagating high-temperature synthesis (MASHS) from elemental powders and sintered by Spark plasma sintering (SPS) technique. The synthesized powders were sintered at three different temperatures of 1400, 1500 and 1600 °C by SPS with 5 min holding time and reached 84, 91 and 99% of the theoretical density, respectively, while the density of the pressureless sintered sample at 1600 °C reached to 86% after 2 h. The phase composition and microstructural analyses show that titanium silicide retained its phase composition and microstructure during the sintering. The mechanical properties of the compound were measured by the Vickers hardness test and nanoindentation technique. The Young's modulus of 268 ± 8 GPa and nanohardness of 16 ± 1.7 GPa were determined by nanoindentation, while the hardness value of 12.5 ± 0.14 GPa was measured by Vickers indentation test. The crack induced by Vickers indenter was used to measure fracture toughness of the compound and the value of 4 ± 0.1 MPa m1/2 was achieved. The transgranular fracture mode can be identified from the fracture surface of the compound.

The plastic deformation processes and fracture mechanisms of as-consolidated powder metallurgy (PM) and as-cast ingot metallurgy (IM) metastable beta titanium alloys (Ti-5Al-5V-5Mo-3Cr) were thoroughly investigated by room temperature tensile tests with in-situ scanning electron microscopy (SEM) observations and further microstructure characterizations including transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results suggested that IM alloy has a better compatible deformation capability than PM alloy characterized by varying slip deformation mechanisms and the constantly changing slip modes. The microcracks in PM alloy were observed to be originated at the interfaces of α″/β and grain boundary α/β. Whereas, the microcracks in IM alloy were observed on the grain boundaries and the intracrystalline α precipitation areas, where the slip steps were generated. Particularly, the common defects in PM (residual pores and microvoids) and IM (casting cavity) alloys did not exhibit significant negative effects, contrary to previous awareness. Finally, the coalescence of the grain boundary α and the widened α″/β microcracks led to the sudden brittle transgranular-intergranular mixed fracture of PM alloy. For IM alloy, the serious cracking initiated the V-shape notch made its way through the microcracks at the α/β slip steps, resulting in the gradual transgranular fracture with better ductility.

Commercial programs using finite element analysis (FEA) have been developed for casting design process. However, their applications have been limited mostly during the casting design stage. This paper explores the possibility of using casting design software for failure analysis. An impeller was failed during services by impact load. The fracture occurred at the thin shroud area of the impeller and showed brittle appearance. Hardness test shows differences of hardness number between thin area (shrouds) and thick area at the impeller, resulted from microstructure differences at the impeller. Shrouds area contained high percentage of graphite (type B) and several undercooled phases (type D graphite) which is typical result for high cooling rate solidification. This microstructure reduced the mechanical properties. SEM examination shows transgranular fracture which is typical for brittle fracture mechanism and reveals higher graphite content at shrouds. Accumulation of titanium, calcium and silicon at the center of graphite was detected using EDAX. FEA simulation using Z-CAST confirms the development of microstructure differences which are substantially affected by casting designs and solidification characteristics.

The mechanical behavior of cast nickel-based superalloy Inconel 718 was investigated via hot tensile experiments at 650 °C, 800 °C, and 950 °C to understand the thermal instability of its metallurgic microstructure. Test specimens, which were machined from investment casting, were subjected to a standard heat treatment. Post-tensile testing, microstructure characterization, and fractography observations were conducted with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The resulting data revealed that the deterioration of toughness and ductility occurred at temperatures above 650 °C. Numerous shear bands and lattice mismatch suggested that plastic deformation through slip movement dominated the ductile fracture mode of the nickel-based superalloy at 650 °C. In contrast, surficial microporosity and grain boundary weakening caused early brittle rupture, before the material yielded, at 800 °C. Significant strain accumulation within grains contributed to plastic flow in the direction of the applied stress load, resulting in intergranular and transgranular fracture at 950 °C. Microstructural evidence displayed the interface debonding between the carbide and the matrix at 950 °C, indicating the temperature limitation of the carbide pileup.

In this work, quasi-in situ tensile unloading and electron backscatter diffraction (EBSD)-based slip trace analysis were applied to study the room-temperature deformation behaviour of Ti 22Al 25Nb alloys with three different microstructures and the plastic deformation mechanism of the B2, α2, and O phases. In addition, the interaction model of the three phases was presented. The results showed obvious B2 slip deformation in the necking region of the B2+α2 microstructure and the B2 texture+α2 samples. The cracks expanded along the regions with low grain boundary density, and the fracture mode was transgranular fracture. The B2 texture improved the harmony and uniformity of the slip deformation between different grains, obviously improving ductility. Owing to the obstruction of the O phase to the B2 phase slip, the B2+O+α2 sample generated an obvious deformation strengthening effect, had no necking phenomenon, and it was also transgranular fracture. The B2 phase slip deformation mode included single system, double system, tri-system, and cross slips. The B2 phase induced a small number of the α2 phases to experience basal slip ((0001) [11–20]) and cracking. The O phase had two deformation modes: (001) plane slip and twin that had (021) as a twinning plane. Two of the 24 slip systems of the B2 phase {110} and {112} can induce an O phase (001) plane slip, 12 systems whose slip direction formed a 54.7° angle with the (001) plane can induce an O phase twin, and other 10 systems cannot induce O phase deformation.

The tensile properties, microstructures and fracture behaviors of an Al-Zn-Mg-Cu alloy during ageing after solution treating and cold-rolling have been investigated. Tensile results show that high strength and acceptable ductility can be achieved simultaneously for the alloy. The enhanced strength, resulting from the combination of high-density dislocations, increased rolling textures, refined grains and nano-sized precipitates, changes with the precipitation characteristics and decreased dislocation densities. The improved ductility is attributed mainly to the decreased dislocation densities and meanwhile influenced by precipitation characteristics. The tensile fractographies are dominated by the dimple-induced transgranular fracture accompanied by small amount of intergranular fracture.

The TiB2-x vol% TiN-20 vol% (Fe-Ni) system cermets with various volume fraction of TiN were successfully fabricated through gas pressure sintering. The effects of TiN content on the mechanical properties and microstructure of TiB2-based cermets was explored in detail. The microstructure and compositional analyses of TiB2-based cermets were investigated by SEM, EPMA, TEM, and X-ray diffraction. The results shown that only TiB2, TiN and Fe0.64Ni0.36 phases in the TiB2-based cermets, not any other brittle phases such as M2B, M23B6 could be found. The TiB2 grains formed a typical core-rim structure, but the TiN particles didn't. The dominant fracture mode of TiB2-based cermets transformed from intergranular fracture to transgranular fracture as the TiN content increasing from 0 to 25 vol%. Toughening mechanisms of TiB2-based cermets transformed from debonding, crack deflection to crack bridging and crack deflection as the TiN content increasing. The properties of TiB2-based cermets have been greatly enhanced as the TiN content varying from 0 to 25 vol%. The transversal rupture strength, indentation fracture toughness, Vickers hardness, and relative density of TiB2–20 vol% TiN-20 vol% (Fe-Ni) cermet reached up to 1191.12 ± 40 MPa, 18.77 ± 0.40 MPa m1/2, 14.40 ± 0.20 GPa, and 99.74 ± 0.20%, respectively.

The creep behavior, creep damage and creep life of 718Plus alloy were investigated at temperatures ranging from 650 to 750 °C in air. The fracture surface, microstructure evolution and deformation mechanisms were studied by optical, scanning and transmission electron microscope (SEM and TEM). The results show that creep curves of 718Plus alloy consist of primary stage and tertiary stage without steady-state region. The Monkman-Grant relationship of 718Plus alloy can be described by tr = 9.32E-2/( e min)0.75 and apparent creep activation energy of 718Plus alloy is about 572.7 kJ/mol. Further investigation shows creep damage of alloy at 650 °C can be mainly ascribed to the effect of grain boundary sliding (GBS) and microtwinning. The alloy shows transgranular fracture at high stress, while it presents ductile fracture at low stress due to the nucleation, growth and linkage of creep voids. At 750 °C, the alloy failed in the form of ductile fracture mainly due to the microstructure instability and dislocation glide. At higher stress of 700 °C, the effect of GBS is mainly responsible for the creep damage of 718Plus alloy, while GBS, dislocation glide and microstructure instability work together and lead to the creep damage of alloys at lower stress of 700 °C. The fracture mechanism map and fracture models for 718Plus alloy were constructed. Remaining life assessment of 718Plus alloys was also evaluated by Larson-Miller parameter method.

Spark plasma sintering (SPS) system was used to develop Ni-17%Cr alloys using nickel and chromium as the raw elemental materials. The powders were fabricated at different sintering temperatures ranging between 800 and 1100 °C, at constant pressure of 50 MPa, heating rate of 150 °C/min and holding time of 10 min. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers microhardness tester and Archimedes’ method were used to investigate the effect of sintering temperature on its microstructure, phases, mechanical properties, densification and fracture mode. The results showed that the relative density, microhardness and fracture morphology of the alloy were affected by sintering temperature, which also affects the microstructure. The maximum relative density of 98.2% and hardness value of 296.33 HV1.0 were obtained at sintering temperature of 1100 °C. The fractography results revealed that the sintered alloys were characterized by transgranular fracture from 900 to 1100 °C.

P92 steel is a potential candidate for ultra-supercritical (USC) plant component. Thus, its suitability and performance for future service are still under investigation. Understanding the creep behaviour is essential to design the components that can sustain in service over a certain period. With the intention to investigate the creep deformation and rupture behaviour of P92 steel weldment, four cross-weld creep specimens were prepared and tested at 600°C at different stress levels. All specimens ruptured between 400 and 4,000 hours. Following the creep test, fractography examination was performed. P92 steel weldment exhibits clear primary, secondary and tertiary creep deformation stages. At long-term, the time portion for primary deformation as compared to rupture time reduces, however, secondary stage is observed to dominate. Deformation and rupture data obeys the power law relation which indicates the material deforms at a higher rate and rupture earlier as the stress increases. Ductility of P92 steel weldment reduces as the stress decreases. A strong correlation between minimum creep strain rate and time to rupture is observed when the data is fitted using original Monkman-Grant (MG) and Modified Monkman-Grant (MMG) relations. Examination of fracture surface reveals that at high stress, transgranular-type of fracture is dominant. As creep time increases, a mixture between the intergranular and transgranular fracture is evidence.

The underlying micromechanism remains to be clarified for the bulk inelastic behaviour of specific ceramics under impact loads. In this study, the silicon carbide materials were subjected to the split-Hopkinson pressure bar compression in which the strain rate was not constant but increased to the dynamic level at high stresses. The inelastic deformation occurs in the high strain rate stage in compression, followed by the final transgranular fracture. The post-test fragments were examined in both the SEM and high resolution TEM. It was found that macroscopic inelastic behaviour is dominated by the dislocation motion and the localised amorphisation that arise at high strain rates. The damage and thus the degraded modulus in the dynamic inelastic deformation were incorporated to modify a dynamic fragmentation model to evaluate the fragment size as a function of strain rates. The modified model more accurately predicts the size of fragments produced at high strain rates. Keywords: Silicon carbide, Inelastic deformation, Fragmentation, Dislocations, Amorphisation

To explore the influence of sintering temperature on mechanical properties of Al2TiO5 (AT) flexible ceramics, the XRD/Raman, SEM and acoustic emission (AE) technology were used to estimate the phase composition, microstructure evolution and damage behaviors of AT ceramics, respectively. Results show that the diffraction peaks of AT increase before rising sintering temperature from 1300 °C to 1500 °C and then start to decrease at 1600 °C due to the decomposition of AT grains. In specimens with sintering temperature of 1300 °C and 1400 °C, intergranular fractures are more likely to occur, which controls the origination of AE events in the whole stage. And the fracture of big bodies composed by large number of fine AT grains is the main source of AE events with high energy level at initial stage. In addition, Thanks to the more transgranular fracture in specimens with sintering temperature of 1500 °C and 1600 °C, the number of AE events in these two specimens are more than that of specimens with sintering temperature of 1300 °C and 1400 °C.

In this work, the crack propagation behavior and mechanism of dual-phase steel were studied under low temperature environment. The results show that the strength of dual-phase steel increases from −20 °C to −60 °C, and the fracture toughness presents the opposite trend. When the crack began to extend at low temperature, the size of plastic zone at the crack-tip is reduced, inducing the opening displacement rate, strain rate and temperature-strain parameters are reduced, which shows the extreme sensitivity to ambient temperature. More importantly, the fracture of dual-phase steel presents the transgranular fracture along {1 0 1} and {1 1 1} crystal planes, due to the accumulation of dislocation density. Therefore, the crack propagation of dual-phase steel at low temperature is caused by the dislocation accumulation and movement behaviors.

International audience; In this article, we reported a processing route for fabricating extremely uniform and ultrafine Zr(Y)O2 particles diffusely distributed in the tungsten matrix. More than 90% of oxide particles are between 100 and 650 nm in diameter. The refinement mechanism of Zr(Y)O2 particles was discussed. Under TEM observation, lots of Zr(Y)O2 particles with a diameter of less than 50 nm are dispersed in tungsten matrix. HRTEM analysis reveals that the Zr(Y)O2 particles exhibit a good bonding with the tungsten phase, but without coherent relation at interface. The fabricated W alloy reinforced by 0.25wt% Zr(Y)O2 exhibits excellent compressive strength of 1577 MPa and fracture strain of 0.262, higherthan those of the pure W and the published experimental results. The fracture surface mainly consists of transgranular fracture and involvessignificant W grain tearing and grain deformations, confirming the strengthening effect caused by nanosized Zr(Y)O2 particles. The hotdeformation behavior of W-Zr(Y)O2 alloy at high temperature was investigated through establishing constitutive equation based on theArrhenius model.

The Mo-10Si-(0, 5, 10, 15)B (at.%) alloys located in Moss (Mo solid solution) +Mo3Si +T2 (Mo5SiB2) region were prepared by arc melting. The effect of B content on the microstructure, microhardness, fracture toughness and oxidation resistance of the alloys was studied. In the Mo-10Si alloy, there are primary Moss and peritectic Mo3Si phases. With the addition of B, (Moss + T2) binary and (Moss + T2 + Mo3Si) ternary eutectics emerge in Mo-10Si-(5, 10)B alloys. For Mo-10Si-15B alloy, primary Moss disappears and the microstructure is only composed of binary and ternary eutectics. With the increase of B content, the proportion and grain size of Moss decrease. The microhardness of alloys increases with the increase of B content due to the increasing intermetallics. The fracture toughness of alloys decreases obviously in single-edge notched three-point bending testing (SENB) and the fracture mode transforms from transgranular fracture to intergranular fracture because of the refinement of Moss. In the high-temperature oxidation test at 1250 °C, the oxidation weight loss of the alloys decreases with the addition of B due to the densification of the borosilicate layer.

The influence of peak compressive stress on the dyamic tensile fracture (spall) in a multi-phase steel, austenite, ferrite and martensite phases, was investigated in as-received and pre-strained conditions. Plate impact experiments were done at ⁓3.0 GPa and ⁓6.0 GPa compressive peak stresses. Results showed that peak stress increase results in about 20% increase in the spall strength for samples tested in the as-received condition, and about 15% increase for the pre-strained samples. These increases could be related to the effects of peak stress on the tensile stress that causes spallation. However, introducing plastic deformations in the pre-strained samples had negligible effects on the spall strength. Microstructural examinations revealed that incipient spall damage was parallel to the phase boundaries and mainly accommodated by ferrite grains as quasi-cleavage transgranular fracture. Samples shocked in the as-received condition with full spallation experienced a quasi-cleavage fracture within the ferrite compared with a cleavage fracture within the ferrite for samples shocked in the pre-strained condition. Deformation within the austenite phase due to plate-impact testing was dependent on the initial sample condition, the pre-strained samples showed more deformation than the as-received samples.

A TiAl–Nb alloy was prepared by casting, and its tensile properties and microstructure evolution at different temperatures were investigated. The results show that the brittle-ductile transition temperature (BDTT) of the alloy is 880–920 °C. At low temperatures, deformation mainly occurs in the γ lamellae and coarsening γ phase between the lamellar colonies. As the temperature increase in the transitory stage, a small number of dislocations may pass through the interface from the coarsening γ phase into the γ lamellae. During the brittle stage, the dislocation and dislocation array bow out from the phase interface, and twins are emitted from the phase interface, which may contribute to the accommodation of stress concentration. During the ductile stage, the γ lamellae coarsen due to the thinner and smaller α2 lamellae dissolving and phase boundary transfer. The dislocations interact with the dislocation walls to form subboundaries in the γ lamellae and transform into equiaxed crystals by dynamic recrystallization (DRX), which increases the plasticity of the alloy. With the transition from the brittle model to the ductile model, the fracture mode of the alloy changes from the mixed fracture mode of transgranular fracture and translaminar fracture to intergranular fracture.

A twinning-induced plasticity (TWIP) steel was prepared by mechanical alloying and spark plasma sintering (SPS), and its microstructure and mechanical behavior were examined. The ultrahigh microhardness and considerable tensile strength of the sintered bulk sample were mainly attributed to grain-size strengthening and particle strengthening by numerous Mn-rich particles dispersed in the matrix. Micropores coupled with large internal inclusions easily produced cracks in the bulk sample under uniaxial tensile stress, resulting in poor ductility with rapid intergranular brittle fracture. The ductility of the material showed significant improvement with the elongation increased from 4% to 13% after annealing the bulk sample at 850 °C for 1 h. The size of the inclusions in the annealed sample dramatically reduced and several small dimples with high densities and depths were formed, presenting a mixed fracture mode in which intergranular fracture was the dominant mechanism, whereas transgranular fracture was the supplementary mechanism.

The research of Nickel-based superalloys with excellent mechanical properties is of significance for aerospace. Here we report the effect of sintering temperature of 850 °C, 900 °C and 950 °C with the heating rate of 100 °C/min via spark plasma sintering (SPS) on Inconel 718 (IN718) superalloy reinforced with 0.25 wt. % reduced oxide graphene (RGO). The microstructures and mechanical properties of IN718-RGO composite were investigated by scanning electron microscopy (SEM) and MTS servo hydraulic testing machine, respectively. SEM results demonstrate that the RGO is almost uniformly distributed into the IN718 powders after 3D rock-milling for 8 h. The mechanical properties of the composite increase with increasing the sintering temperature. When the sintering temperature is 950 °C, a relative density of 92.5%, a microhardness of 375 Hv and an ultimate compressive strength of 1748.20 MPa after aging heat treatment was obtained for the IN718–0.25 wt. % RGO, respectively. The fracture mechanism of the composite changes from intergranular fracture to transgranular fracture with the sintering temperature increasing.

Effects of creep aging on strength and toughness and microstructure evolution of Al-Cu-Li alloy were investigated by tensile test and Kahn tear test at room temperature, combined with fractograph and transmission microstructure analysis. The specimens of pre-strain creep aging state (CA) have been studied and compared with artificial aging state (AA) and pre-strain artificial aging state (PA). It is demonstrated that pre-strain before artificial aging process can improve the strength property and the fracture toughness of Al-Cu-Li alloy. On top of that, both of them can be further improved by creep aging process: the yield strength was increased by 8.7% and the unit initiation energy of Kahn tear was increased by 11.7%. The increasing of fracture toughness has also been verified by Kahn tear fractographs that the dominating fracture type changes from the ductile intergranular fracture to the ductile transgranular fracture. Transmission electron microscopy revealed that creep aging promotes the nucleation of T1 phase, resulting in a fine and dense distribution of precipitates in the matrix, and the enrichment of subgrain boundary T1 precipitates was greatly reduced.

The hydrogen embrittlement of 12Cr2Mo1R(H) steel at different strain rates were investigated after hydrogen precharging for 4 h in a 0.5 M H2SO4 solution with 2 g/L ammonium thiocyanate. Results showed that the embrittlement index increased and gradually reached a relative stable value of about 20% at the strain rate of 5 × 10−5 s−1 with the decrease of strain rates. SEM images depicted small and deep flakes at high strain rates, while flakes grew larger at slow strain rates. Most hydrogen-induced cracks (HICs) were transgranular fracture through lath grain of bainitic ferrite. High strain field surrounds the crack tips, which makes the crack tips of two close and parallel cracks deflect toward each another and even form crack coalescence. The electron backscatter diffraction technique was used to investigate the effects of grain boundaries, recrystallization fraction, kernel average misorientation map, texture component, and coincidence site lattice boundaries on the HIC propagation. High densities of dislocations and strain concentrations were found around the cracks, where grains are highly sensitive to HIC.

Effects of HfN content and metallic additives on microstructure and mechanical properties of TiC 0.7 N 0.3 -based ceramics were investigated. HfN had very weak inhibition effect on TiC 0.7 N 0.3 grain growth. When HfN content increased from 10 wt% to 20 wt%, flexural strength and fracture toughness became higher, but Vickers hardness was around 20 GPa without significant changes. The optimal mechanical properties of TiC 0.7 N 0.3 -20 wt%HfN-Ni-Co were that Vickers hardness was 18.93 GPa, flexural strength was 876.17 MPa and fracture toughness was 7.58 MPa m 1/2 in this investigation. Ni-Mo additive exhibited better wettability with TiC 0.7 N 0.3 than the other metallic additives. Ni-Mo additive could inhibit TiC 0.7 N 0.3 grain growth effectively and improve mechanical properties of TiC 0.7 N 0.3 -based ceramic. The optimal mechanical properties of TiC 0.7 N 0.3 -20 wt%HfN-Ni-Mo ceramic was that Vickers hardness was 19.43 GPa, flexural strength was 1235.88 MPa and fracture toughness was 8.46 MPa m 1/2 in this investigation. Its toughening mechanism mainly included crack deflection and crack bridging. In addition, the mixed intergranular/transgranular fracture also could improve fracture toughness.

The three-point bending test was performed on cemented tailing backfill prepared with different offset notches by a loading system with high-speed camera. And the effect of heated temperature on CTB fracture behavior has been investigated. These results indicate that the influence of pre-existing notch and temperature on CTB fracture feature is obvious. The peak load increases linearly with the increasing of the offset ratio when the depth-height ratio of notch is fixed at the same value, while the fracture peak loading decreases sharply with the increase of the notch depth when the offset ratios are the same level. The fracture toughness decreases by 63.5% as the heated temperature rises from 20 °C to 120 °C. The fracture toughness is directly proportional to the porosity of CTB. The increasing of porosity leads to the decrease of the fracture toughness mainly due to the decomposition of hydration products and the coarsening of the pore structure of CTBs. The crack propagates along the interface among tailing particles, resulting in a rough and jagged edge propagation path. The rack propagation pattern of CTB samples contains transgranular fracture and intergranular fracture. The intergranular fracture is clearly predominant during crack propagation. The rack propagation and failure pattern of CTB specimens from numerical modeling are conformed to the failure pattern of samples obtained by experimental testing. PFC is an effective numerical analysis method for exploring the fracture mechanism of micro-cracking in CTB.

This paper reports a study on mechanical behavior during tensile testing of nanostructured (NS) Al and ultra-fine grained (UFG) Al containing nanoscale oxide particles that were produced via consolidation of nano-sized Al powders using spark plasma sintering (SPS) only and SPS plus extrusion, respectively. Our results show that the NS Al exhibits ∼370 MPa in 0.2% offset yield strength and ∼0.9% in elongation to failure, whereas the UFG Al presents ∼430 MPa in 0.2% offset yield strength and ∼1.5% and ∼1.9% in uniform elongation and elongation to failure, respectively. Based on the tensile stress vs. strain curves, microstructural features and fractured surface characteristics, mechanical behavior of NS Al and UFG Al was analyzed and discussed in detail. We suggest that the lower yield strength and ductility in the NS Al than those in UFG Al can be attributed to the strong stress concentration at grain boundaries (GBs) as a result of (i) the presence of highly segregated nanoscale oxide particles and of residual porosity at GBs to induce, and (ii) the absence of dislocation sources and thus of activated dislocation slip at nano-sized grain interiors (GIs) to release, the stress concentration. Immediately after yield in the as-SPSed Al, the stress concentration debonded GBs and further tensile straining rapidly led to connection between debonded GBs and the occurrence of intergranular fracture. In contrast, in the UFG Al the extent of oxide particle segregation and the porosity at GBs were reduced due to materials flow during extrusion, avoiding the occurrence of intergranular fracture at a very low strain level and thus sustaining plastic straining; as a result, yield strength and ductility were improved. However, the residual porosity and nano-sized/ultra-fine grains still induced early strain localization shortly followed by transgranular fracture via growth, coalescence and connection of nano-sized pores, leading to limited ductility.

Edge-on impact experiments on AlON, a transparent ceramic with superior ballistic performance, show combined intergranular and transgranular fracture. An initial fast-propagating damage front transitions into slower-propagating localized cracks. We develop a peridynamic model for polycrystalline AlON to investigate the failure evolution observed in experiments. We use a computational polycrystalline structure with the same average grain size as the samples used in experiments. The peridynamic model helps explain the reasons behind the observed failure front supershear propagation speed (higher than 2 times the shear wave speed), and the subsequent transition to sub-Rayleigh propagating localized cracks. The computed propagation speeds for the damage front, and the cracks that emanate from it, match very well those measured in experiments. Elastic anisotropy, material microstructure, and brittle failure are the only ingredients used here to determine damage evolution in edge-on impact on brittle polycrystalline materials, under no confinement. Other possible dissipation mechanisms, like twinning, plasticity, friction, are not included in the model. These are likely second-order effects in the evolution of damage and failure for this material and at these impact speeds.

The design of metallic alloys with superior properties requires a deep understanding of the atomistic processes governing the materials behavior. In this paper, we present results providing a close link between grain boundary (GB) chemistry and fracture behavior in a Mo-Hf alloy. By combining atom probe tomography and ab-initio simulations of GBs, we unravel the origin for the transition between intergranular and transgranular fracture in technological Mo-Hf alloys. The main agent affecting GB strength is not the primary alloying element Hf, but rather the impurities O, C and B. With larger Hf additions, an intricate interplay between segregation and precipitation leads to a strong GB enrichment of C and B and to a depletion of O and Hf resulting in a higher cohesion of the GBs and thus, leading to a change in fracture mode. Our investigation exemplarily demonstrates that smallest additions of solutes can be decisive for understanding fracture behavior on the macroscale. Keywords: Atom probe tomography, Density functional theory, Grain boundary engineering, Intergranular failure, Molybdenum

Susceptibility to hot shortness and hot cracking of Cu bearing steels is generally minimized with the addition of Ni. However, in this study, attempts have been made to reduce the hot working problems in such steels by the addition of Si, P and either very low content of Ni or no Ni, which will be understood after evaluating their hot ductility and hot shortness properties. The main techniques employed for this study are hot tensile test, analysis of fractography and characterization of scale/steel interface after long exposure at high temperature. The steels having 0.80–0.86% Si exhibited adequate hot ductility at all deformation temperatures ranging from 850 °C to 1200 °C during slow strain rate (0.005 s−1) testing conditions and the fracture morphology exhibited both ductile conical dimples and transgranular fracture. On the other hand, ~0.40% Si containing steels exhibited significantly reduced hot ductility at 850 °C and failed in intergranular brittle fracture mode. The improved hot ductility of high Si containing steels is explained using Fe-P phase diagram along with the proposition of inverse segregation of Si and repulsive interaction between P and Si. On increasing strain rate to 6.5 s−1, ductile failure was observed in all steels. The long duration of soaking at 1200 °C lead to intergranular decohesion and hot tearing during tensile testing in ~0.12% and ~0.19% P containing steels, respectively. A separate study of oxidation in air at 1200 °C indicated that presence of ~ 0.12% P in steel is beneficial in reducing hot shortness by keeping Cu enriched phase away from the scale/steel interface. In contrary to this, oxidation of ~0.19%P containing steel is detrimental to hot working as the grain boundaries of this steel were severely oxidized to the depth of few grains. Other alloying elements such as Ni and Cr in experimental steels had no effect on hot ductility and hot shortness properties.

The influence of pre-stretching and aging treatment on the mechanical properties and corrosion behavior of 7050 alloy were studied by tensile testing, potentiodynamic polarization, and intergranular corrosion (IGC) testing associated with optical microscopy (OM), scanning electron microscopy, and transmission electron microscopy. The results exhibit both strength and elongation of T6 are higher than T74. The strength of retrogression and re-aging (RRA) samples are equal to or even in excess of T6 sample, especially, the strength of RRA-60 sample increased by 5.7% at the sacrifice of its elongation. Both yield strength of T651 and RRA51-60 samples with 4% pre-stretching are enhanced while their elongation decreased too much. The fracture feature of T6 and T651 samples are majorly intergranular fracture, while the fracture mode of RRA samples are mainly transgranular fracture. The corrosion resistance of T74 could be significantly improved through IGC tests and electrochemical polarization tests. Al...

Commercially pure (CP) titanium with a bimodal harmonic structure, which is defined as coarse grained regions surrounded by a network of fine grains, was fabricated by consolidating mechanically milled powders to improve both strength and ductility. In order to determine the fatigue properties of bimodal harmonic structured CP titanium, four-point bending fatigue tests were conducted at a stress ratio of 0.1 under ambient conditions. The fracture surfaces were analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to identify the mechanisms of small fatigue crack initiation and propagation on the basis of fractography and crystallography. The fatigue crack initiation resistance was increased compared to sintered compacts fabricated from as-received initial powders, which was attributed to grain refinement during mechanical milling. Transgranular fracture occurred from coarse grains with a basal plane perpendicular to the loading direction. The fatigue crack path in harmonic structured CP titanium was not influenced by the microstructure.