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In this paper, the microstructure and mechanical properties of Al-6.5Si-5.5Cu-0.2Zr-0.01Sr-0.06Ti-0.2Ce cast aluminum alloys were investigated in multistage solid solution systems. The microstructure of the alloy was characterized using an optical microscope (OM), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), x-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. The hardness and conductivity of the alloy were measured using a Vickers hardness and eddy current conductivity testers, respectively, and the tensile properties were described by a drawing machine. The results showed that the mechanical properties of the alloy are the worst under the four-stage solid solution system (G1). With the increase in multistage solution temperature and holding time, θ phase (Al2Cu) was gradually dissolved into α-Al matrix to enhance the effect of dislocation strengthening. When the solution temperature reached 510 °C, the mechanical properties of the alloy were the best, and the tensile strength and elongation were increased to 354.90 MPa and 9.02%, respectively. With the increase in temperature, eutectic Si agglomeration and large area of insoluble phase between metals were found, resulting in the decrease in mechanical properties. [ABSTRACT FROM AUTHOR]

The effects of alloying elements on the microstructure evolution and properties of GH2107 superalloy during long-term aging are investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The results indicate that the microstructure of the alloy becomes unstable with the prolongation of aging time. Cr element promotes the precipitation of M23C6 carbides at grain boundaries, and Fe element inhibits the precipitation and growth of M23C6 carbides at high temperature. At the same time, high Fe promotes the growth of γ' phase and the precipitation of TCP phase, which has a certain influence on the plasticity and strength of the alloy. The yield strength of alloy1 (15.41% Cr, 35.3% Fe) and alloy2 (15.08% Cr, 40.1% Fe) decreases with the increase in aging time. However, for alloy3 with high Fe content, the yield strength increases suddenly at 3000 h aging time due to the improving effect of solid solution strengthening. In addition, the dislocation movement mechanism of GH2107 alloy was studied, and Orowan bypass mechanism is more likely to occur in alloys with high Fe content. [ABSTRACT FROM AUTHOR]

The stability of microstructure and performance after long-term service are crucial for the engineering application of ASME SA335-P92 steel. In this present work, a series of isothermal aging tests for P92 steel were performed at 680 °C as long as 21,000 h. Microstructure at different stages of evolution was characterized using scanning electron microscope and transmission electron microscopy. Strength and plasticity measurements under the static mechanical tensile condition were also carried out at room temperature. Results showed that Laves phases precipitated rapidly at the early aging stage and coarsened with a relatively high rate in the followed aging period, while M23C6 carbides were precipitated continuously during the aging process. The tensile strength and plasticity of P92 steel at room temperature declined rapidly at the early stage of aging. During the afterward aging process, strength overall presented a slowly falling tendency but plasticity remained a sustainable stability. Micro-mechanism of variation on mechanical tensile properties for P92 steel aged for a long-term time would be further revealed in this paper. [ABSTRACT FROM AUTHOR]

Dense Ti-48Al-2Cr-2Nb-xGd (x = 0, 0.15, 0.3 at. %) alloys with different compositions were prepared by spark plasma sintering (SPS). The phase composition and microstructure of sintered alloys were studied by x-ray diffraction analyzer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The mechanical properties were determined by room-temperature compression test. Results show that Gd2O3 and Al3Gd are the gadolinium-rich precipitates formed at the boundary of the original powder particles after the addition of Gd. However, with the increase in Gd addition, the precipitates will gather and grow together, and the dispersed fine precipitates play the role of dispersion strengthening, while the large particles gathered together play the opposite role. The TiAl alloy added with 0.15%Gd has the best compressive properties, and the ultimate compressive strength and fracture strain are 2750 MPa and 43.59%, respectively, which are significantly better than the cast alloy and the alloy without Gd. [ABSTRACT FROM AUTHOR]

In the present study, the effect of different accumulative roll bonding (ARB) process routes was investigated on microstructure and mechanical properties for commercially pure copper strips. Scanning electron microscope equipped with EBSD detector, optical microscope, tensile and hardness tests were used. Copper strips were ARBed up to 8 cycles both in route A (conventional ARB) and also in route BC (rotated 90° anti-clockwise before each cycle). Higher bonding quality was achieved when strips ARBed in route BC. However, tensile strength increased in both routes by proceeding ARB process. The orientation maps of specimens subjected to route A showed bimodal grain size, whereas the ones ARBed in route BC, a relatively equiaxed grain, were obtained. Rotation of specimens between different cycles (i.e., route Bc) resulted in lower strength as a result of lower dislocation density as well as lower accumulative strain hardening. Fractography results showed that by increasing the number of ARB cycles, the failure mode in the specimens changed from a ductile fracture to a shear–ductile fracture with shear dimples. [ABSTRACT FROM AUTHOR]

In this paper, the Nb-containing duplex stainless steel (DSS) was prepared using the tungsten inert-gas welding powder surfacing method, and the solution treatment was carried out at different temperatures. A scanning electron microscope with an energy-dispersive spectrometer, universal testing machine, and ultrasonic cavitation equipment were used to study the structure, mechanical properties, and cavitation erosion (CE) resistance of DSS. The results showed that, compared with the as-welded 2209 DSS, Nb-containing DSS has better strength and lower plasticity. After heat treatment, the strength and plasticity of Nb-containing DSS were also reduced. During the ultrasonic CE test, the cumulative weight losses of the Nb-containing DSSs for 6 h were less than that of the control group (2209 DSS). However, solution treatment caused the Z phase to appear in the Nb-containing DSSs. Z phase reduced the mechanical properties of the matrix, promoted the initiation of CE cracks, and increased the cavitation weight loss of the sample after heat treatment. [ABSTRACT FROM AUTHOR]

In this paper, pure W was successfully brazed to itself using self-prepared Ti-35Ni filler alloy. The scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and x-ray diffractometry (XRD) were utilized to characterized the interfacial microstructure. The results showed that the typical interfacial microstructure of W-W joint was: W substrate/W containing Ti-Ni intermetallics/TiNi+Ti2Ni+Ti(s,s)+W particles/W containing Ti-Ni intermetallics/W substrate. The brazing temperature presented a pronounced influence on the interfacial microstructure and mechanical properties of W-W joints. With increasing brazing temperature, the thickness of brazing seam was gradually reduced while the diffusion zone became widened. The disappearance of the defects was also observed. The shear strength of W-W joints tested at room temperature and at 800 °C was up to 74.87 and 214.08 MPa, respectively. The fracture surface presented a mixed characteristic of cleavage and trans-granular fracture. [ABSTRACT FROM AUTHOR]

A novel aluminum matrix composites (AMCs) reinforced by multiphase intermetallic compounds were fabricated through a conventional casting approach. The microstructure, compression properties and tribological behavior of the AMCs were detailed studied by the scanning electron microscope (SEM), x-ray diffraction (XRD), and electron probe microanalysis (EPMA). The results demonstrated that the fraction of precipitated multiphase intermetallic compounds gradually increased with the increase of high-entropy alloy (HEA) adding content, and the grain size of α-Al obviously was reduced. The irregular multiphase intermetallic compounds, such as Al70Cr20Ni10 and AlTiCrSi, are distributed in the Al matrix. However, the Al2Cu and Al7Cu4Ni distributed in inter-dendrites of α-Al. In addition, the compression strength of AMCs reinforced by 20.0 wt.% HEA addition was significantly enhanced to 530 MPa due to the precipitation of multiphase intermetallic compounds. Meanwhile, its compression strain was higher than 25%. Compared with pure Al, the microhardness of AMCs was extremely increased to 160 HV when the addition content of HEA was up to 20.0 wt.%. When the addition amount of HEA reached 10.0 wt.%, the COF of the ACMs was decreased by 51.6% from 0.766 to 0.371. When the HEA content was up to 20.0 wt.%, the wear rate reached the minimum of 4.87 × 10−5 mm3/N·m, which was reduced by 31.9% compared with pure Al. Furthermore, the strengthening effect and wear mechanism of AMCs reinforced by HEA addition was also discussed. [ABSTRACT FROM AUTHOR]

The effects of Ag content and hot-rolling on the microstructure and mechanical properties of Zn-1.5Cu-xAg-0.1Zr(x = 0, 0.1, 0.5, 1.0) alloys were investigated. The microstructure, phase composition and fracture morphology of the alloys were observed and analyzed by optical microscope, x-ray diffraction, scanning electron microscope, energy dispersive spectrometer and universal mechanical testing machine. The results show that Ag has the effect of grain refinement. After alloying, the grain size of as-cast Zn-1.5Cu-xAg-0.1Zr alloy decreased first and then increased, and the minimum grain size of as-cast Zn-1.5Cu-0.5Ag-0.1Zr alloy was refined to 64.18 μm. At the same time, new phase AgZn3 began to precipitate, the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of alloys were also up to 97.35 MPa, 139.25 MPa and 7.60%, respectively. After hot-rolling, the grain of Zn-1.5Cu-xAg-0.1Zr alloy was broken and new phase CuZn5 was precipitated. The mechanical properties were significantly improved, and the maximum YS, UTS and EL of as-rolled Zn-1.5Cu-1.0Ag-0.1Zr alloy were 218.14MPa, 244.83MPa, 64.50%, respectively. [ABSTRACT FROM AUTHOR]

Because of low cost, high material forming efficiency and utilization, wire arc additive manufacturing (WAAM) is widely used in the manufacture of large components in the past ten years. However, the directional heat dissipation during WAAM stainless steel will cause the growth of coarse columnar grains along the build direction of the components, resulting in strong anisotropy of mechanical properties in WAAM components and reducing its strength. In this paper, nano-SiC grain modifier was added in the WAAM 304 stainless steel to suppress the growth of coarse columnar grains to improve the performance of WAAM components. At first, SiC powder with different particle sizes (100, 300 nm) was made into ethanol-based coatings with mass fractions of 0, 2, 5 and 10 wt.%. During the WAAM process, coating was added layer by layer to make six groups of thin-walled components containing SiC and a group of thin-walled wall components without coating of SiC. Then, microstructure of the components was analyzed through metallographic microscope, X-ray diffraction and scanning electron microscope. The results revealed that the introduction of SiC into the matrix structure promoted heterogeneous nucleation and achieved the effect of grain refinement. As the SiC particle content increased, the matrix grain size further decreased. In addition, mechanical properties and Vickers hardness of the components were tested. The results showed that the ultimate strength and hardness of the SiC-added components were improved, and the anisotropy was reduced. As the SiC content increased, the strength and hardness of the parts increased, which is due to a more refined grain structure. [ABSTRACT FROM AUTHOR]

The development of magnesium alloys with superior plasticity and favorable strength is still challenging in aerospace industry. Herein, hot extruded Mg-xNd-2.0Sm-0.4Zn-0.4Zr alloys (x = 0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) were rationally designed and easily prepared in order to implement the favorable combination of strength and plasticity. The effects of Nd element addition on the microstructure and mechanical properties of the hot extruded alloys were systematically investigated by optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The OM results indicated that the grain size of the hot extruded alloys decreased from 27.1 to 14.1 μm with increasing Nd addition from 0 to 2.5 wt.%. Some coarse β phases existed at the grain boundary when the addition of Nd element increased to 2.0 wt.%. The TEM results showed that the nanoscaled basal lamellar precipitates, granular precipitates and prismatic lamellar precipitates formed in α-Mg matrix. And the amount of precipitated phase increased obviously with the increase of Nd element addition. The ultimate tensile strength increased significantly from 203 ± 3.0 to 237 ± 2.5 MPa, and the elongation decreased from 30.5 to 21.2 % when the Nd elements increased from 0 to 2.5 wt.%. The fractographs of the hot extruded alloys could be classified as ductile fracture. [ABSTRACT FROM AUTHOR]

In this study, 24CrNiMo samples with low porosity and high strength were prepared by selecting laser melting technology (SLM). The defect distribution, microstructure evolution, and tensile fracture surface were analyzed by scanning electron microscope and electron backscatter diffraction (EBSD). The experimental results showed that with increase in the energy density, the types of defects would change, and the number of defects showed a trend of first decreasing and then increasing. The microstructure of the samples mainly consisted of martensite with a small amount of lower bainite and residual austenite. EBSD analysis showed that no crystallographic texture was found in the samples. However, the grain orientation would change original direction to form a texture parallel to the load direction during the tensile process. The average grain size increased from 0.346 to 0.381 μm with the increase in energy density. The best sample was prepared under the parameters of 76.56 J/mm3, with the highest microhardness (458.96 HV0.2), ultimate tensile strength (1378.53 MPa), and strength–plasticity product (18.23 GPa%). The relationship among defects distribution, microstructure, and mechanical properties was established, which provided a corresponding theoretical basis for SLM to prepare low-alloy steel. [ABSTRACT FROM AUTHOR]

In welding of high-strength steels by conventional methods, it is essential to preserve the strength and ductility close to the base material. The primary focus of this research was to investigate the electron backscattered diffraction (EBSD) characteristics in the coarse grain heat-affected zone (CGHAZ) of S900 base material and correlate them with the changes of mechanical properties of the welded joints. For this purpose, the S900 high-strength low alloy steel was welded with different heat inputs. The thermal cycles were obtained using the Simufact welding simulation software. Scanning electron microscope and EBSD analyses were used to evaluate the microstructure, and tensile tests were used to assess the mechanical properties. The results showed that reducing the welding heat input changed the failure region from the CGHAZ to the base material. The depression of heat input can decrease the deleterious effect of the welding process and lead to achieving superior mechanical properties for the welded joints. Reducing prior austenite grain size in CGHAZ, forming less granular bainite, and maintaining the dislocation density high enough in CGHAZ were the main reasons for improving the mechanical properties of the joints welded at lower heat input. [ABSTRACT FROM AUTHOR]

In this study, a new alloy material Mg-Zn-Zr (ZK60) was designed for the connecting rod. It was found that the blanks sampled along the vertical direction of an extruded bar crack during the roll forging process. The microstructure and precipitates of the extruded bar were observed and analyzed using optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The result showed that the Zn, Zr, and MnZn2 precipitates were elongated along the extrusion direction. The mechanical anisotropy was investigated by testing the mechanical properties of the specimens sampling from different angles. Hot deformation behavior was further studied using the Gleeble 3500 thermal-mechanical simulator. The tensile and yield strengths were the highest along the extrusion direction, reaching 347 MPa and 301 MPa, respectively. The deformation resistance was also higher in the extrusion direction than that in the vertical direction. Fracture mechanisms of the sample from different directions were discussed. The ZK60 alloy was more susceptible to failure if the deformation direction was parallel to the bands of segregation area and precipitates. [ABSTRACT FROM AUTHOR]

In this paper, different tool pin profiles, namely taper-threaded, triangular, and hybrid are used to join 5-mm-thick 2050-T84 Al-Cu-Li alloy by friction-stir-welding. The experiments were conducted using a one-variable-at-a-time approach by varying the geometry of tool pin profile and kept constant values of tool rotational speed, tool traverse speed, and tool tilt angle as 1400 rpm, 180 mm/min, and 2°, respectively. The objectives of this paper are to determine the effects of varying tool pin profile on force–torque behavior, microstructure, grain size distribution, tensile properties, and mode of tensile failure. It was observed that the hybrid tool produced less flash, less vertical downward force(14340.49N), low average grain size (11.27 µm) in the nugget zone, and larger weld bead area along with higher tensile strength (418.98 MPa), joint efficiency (78.44%), and micro-hardness (147HV0.1) when compared to other tools. The fractography analyses were performed using field-emission scanning electron microscope and observed ductile mode of failure for all friction stir-welded joints. [ABSTRACT FROM AUTHOR]

Corrosion and corrosion-related mechanical behaviors of Ti-microalloyed AZ31 Mg alloy (AZ31Ti) in simulated body fluid (SBF) under a dynamic environment were investigated. AZ31 Mg alloy was used as a control alloy. Microstructure analysis of the samples was performed by using a scanning electron microscope and an x-ray diffractometer. Mass loss measurements and corrosion-related tensile tests were carried out by immersing the samples in the SBF solution at 37.5 ± 0.5 °C for 24, 72, and 336 h under dynamic conditions. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were also employed in the SBF solution at 37.5 ± 0.5 °C. Microstructural studies showed that the β ( Mg 17 Al 12 ) intermetallic phases in the AZ31 alloy are dispersed in the microstructure and formed as relatively angular particles, and that the dimensions of the β phases transformed to a smaller size and globular form with Ti microalloying. While the tensile strength and hardness values of AZ31 and AZ31Ti alloys were similar to each other, Ti microalloying showed a considerable increase in the yield strength and elongation. This study suggests that microalloying of AZ31 alloy with Ti is beneficial in terms of their corrosion resistance and corrosion-related mechanical properties in an SBF environment under dynamic conditions. [ABSTRACT FROM AUTHOR]

In this paper, the hot deformation behavior of A357 alloy was investigated by hot compression tests. Isothermal hot compression simulation tests for A357 alloy were carried out at the conditions of deformation temperature of 350-470 °C, strain rate of 0.001-10 s−1 and engineering strain of 50%. Based on the Prasad instability criterion and dynamic material model, the hot processing maps of A357 alloy were constructed. The microstructure of compressed samples at different areas of the hot processing map was characterized by metallographic and scanning electron microscope and transmission electron microscope. The experimental results showed that the unstable processing zone of A357 alloy was mainly distributed in the high strain rate (10 s−1) and low-temperature (350, 380 °C) region. With an increase in the strain, the unstable zone expanded from low temperature to high temperature (470 °C). The ideal deformation conditions were deformation temperatures of 380-410 °C and strain rates of 0.001-0.01 s−1, and deformation temperatures of 440-470 °C and strain rates of 0.01-1 s−1. When the A357 alloy was extruded with the optimal hot processing parameters, the results suggested that hot extrusion could make the microstructure uniform and fine, thereby improving mechanical properties, especially when the elongation was up to 19.5% higher than the as-cast A357 alloy. [ABSTRACT FROM AUTHOR]

Glass samples with the compositions xFe2O3-35SiO2-35B2O3-10Al2O3-(20 − x) Na2O (0 ≤ x ≤ 1 mol.%) were designed and assembled by melting quenching technique. These samples were investigated by XRD, optical, mechanical, thermal, and FT-IR spectroscopy studies. FT-IR spectra reveal that these glasses are built up of BO3, BO4, and octahedral [FeO6]. The present glasses exhibited the increase in density, thermal parameter values, ultrasonic velocities, elastic moduli, optical band gap (Eopt), and refractive index of the prepared glasses. The corresponding glass-ceramic of these glasses was prepared by controlling heat treatment and investigated with XRD, mechanical, SEM, and TEM. The present glass-ceramics exhibited the increase in density, ultrasonic velocities, and elastic moduli; these values are larger than those of the parent glasses. XRD exhibited the crystalline phases of selected glass-ceramics samples. The transmission electron microscope (TEM) exhibited the grain size of glass-ceramics in nano-size and range between 63.9 and 165 nm. The scanning electron microscope (SEM) exhibited backscattered electron images of the produced glass-ceramics. It is observed that crystalline texture contains relatively large interstitial pores, demonstrating the residual glassy matrix. [ABSTRACT FROM AUTHOR]

There has been great attention on high-entropy alloys (HEAs) over the past decade. Unlike conventional alloy systems, HEAs commonly include at least five principal elements with equiatomic or near-equiatomic ratio. HEAs with their superior mechanical, magnetic, and thermal properties are promising materials for critical engineering applications. Medium-entropy alloys (MEAs), which consist of less than five principal elements, have very similar structural features with HEAs such as robust thermodynamic stability and exceptional mechanical performance. The insights of MEAs have not been fully revealed yet. In the present study, novel MEAs (Cu20Ni20Al30Ti30, Cu25Ni25Al25Ti25, Cu34Ni22Al22Ti22, and Cu35Ni25Al20Ti20) have been designed using thermo-physical calculations and Thermo-Calc software. These MEAs were then produced using copper heart arc melting and suction cast into cylindrical rods with 3 mm diameters. X-ray diffraction (XRD), optical microscope (OM), transmission electron microscope (TEM), scanning electron microscope (SEM), and energy-dispersive spectroscopy (EDS) were used for structural characterization. The corresponding results reveal that the Cu20Ni20Al30Ti30, MEA, consists of a body-centered cubic (BCC-B2) phase with intermetallic compounds (ICs), whereas Cu25Ni25Al25Ti25 has single BCC-B2 phase. When the amounts Cu and Ni are increased, system drives itself toward a face-centered cubic (FCC) structure. A dual BCC and FCC composite Cu35Ni25Al20Ti20 has been detected as the most promising MEA among the others with 820 and 1338 MPa measured yield and compressive strength, respectively. [ABSTRACT FROM AUTHOR]

Phase transformation during intercritical annealing (IA) and the relationship between microstructure and mechanical properties of the intercritical annealed 0.2C-5MnTRIP steels were investigated using a combined method of dilatometry, scanning electron microscope, transmission electron microscope, x-ray diffraction, and tensile testing. With the increase in IA temperature and holding time, the fraction of reversed austenite increases while the chemical stability of reversed austenite decreases, leading to the transformation of reversed austenite to martensite in the cooling stage. IA temperature is found to have a greater influence on the stability of austenite than IA time. The microstructures mainly comprised of ferrite and retained austenite, with granular carbide and martensite also observed in some specimens. The carbide precipitates formed during hot rolling remain after cold rolling and annealing process and gradually dissolve at higher IA temperature or with longer IA time. The optimal IA parameter, i.e., 650 °C for 15 min, contributes to a good product of tensile strength and elongation (997 MPa × 29.25%) due to an excellent TRIP effect. The present work gives a clear insight in controlling the mechanical properties of medium Mn TRIP steel in the continuous annealing line by a reasonable design of the IA process. [ABSTRACT FROM AUTHOR]

The Mg-Zn-Gd-Zr alloy is one of the important aerospace alloys in the aircraft gearbox applications. The complex geometry of the gearbox introduces several stress concentration points with various intensities. These regions are susceptible to catastrophic failure under mixed loading condition. Therefore, it is important to understand the deformation and failure mode of this alloy for various plastic constraint conditions. In the present work, Mg-4%Zn-1.5%Gd-0.5%Zr alloys were prepared with four different increasing notch root radii (1, 2, 4 and 8 mm). These samples were tested for tensile properties and compared with the smooth condition. In addition, notch sensitivity was determined analytically. The microstructure and fracture samples of the alloy were characterized with the aid of an optical/scanning electron microscope. Tensile test results show that the alloy is notch sensitive and shows notch-strengthening effects. The notch strength ratio increases with the decrease in the notch root radius due to the strong plastic constraint. The predicted and experimental results of the fracture strain with the notch root radius are in qualitative agreement. The void growth rate prediction is qualitatively in agreement with the tensile and fractography results and suggests that the notch geometry has a significant influence on the plastic strain of the alloy. The microstructure of the alloy has equiaxed grains of 74 ± 24 µm with the grain boundary eutectic. The eutectic is composed of Gd-rich Mg phase. The fracture surface has a distinct change from mixed mode to complete cleavage with the increasing notch root radius. The fractography results show that the fracture mode is predominantly intergranular for all the cases. [ABSTRACT FROM AUTHOR]

In this study, the effects of compound modification with Bi and Sb and solution treatment on the microstructures evolution and the mechanical properties of Al-20 wt.% Mg2Si composites were investigated. The specimens were observed by optical microscope, scanning electron microscope equipped with an energy-dispersive spectrometer and x-ray diffraction. The characterization results showed that 2.0 wt.% Sb and 0.2 wt.% Bi addition refined the primary Mg2Si from 95 to 10 μm, accompanied by a change in morphology from coarse dendrites to dispersive fine polygons. After solution treatment at 540 °C for 15 h, the sharp polygonal primary Mg2Si particles were blunted and the flake-like eutectic Mg2Si phases were changed to small spherical particles, resulting in the increase in the Brinell hardness of the composites from HB 94.53 to 134.67. Mechanical tests revealed that both tensile strength and hardness of the composite were improved by compound modification with Bi and Sb, and the ultimate tensile strength (UTS) was increased from 216 MPa unmodified to 257 MPa with optimum modification of 2 wt.% Sb and 0.2 wt.% Bi. A propounded change in hardness from HB 94.53 to 130.67 was also investigated. [ABSTRACT FROM AUTHOR]

In the present investigation, friction stir welding of commercially pure aluminum and 304 stainless steel was carried out at varying tool rotational speeds from 200 to 1000 rpm in steps of 200 rpm using 60 mm/min traverse speed at 2 (degree) tool tilt angle. Microstructural characterization of the interfacial zone was carried out using optical microscope and scanning electron microscope. Energy-dispersive spectroscopy indicated the presence of FeAl3 intermetallic phase. Thickness of the intermetallic layer increased with the increase in tool rotational speed. X-ray diffraction studies indicated the formation of intermetallic phases like FeAl2, Fe4Al13, Fe2Al5, and FeAl3. A maximum tensile strength of ~ 90% that of aluminum along with ~ 4.5% elongation was achieved with the welded sample at tool rotational speed of 400 rpm. The stir zone showed higher hardness as compared to base metals, heat affected zone, and thermo-mechanically affected zone due to the presence of intermetallics. The maximum hardness value at the stir zone was achieved at 1000 rpm tool rotational speed. [ABSTRACT FROM AUTHOR]

Ni/Al laminates are of great interest in many aerospace and military applications due to their excellent mechanical properties. However, their application has been limited in part due to challenges related to fabricating complex geometries. However, explosive welding is regarded as a promising technique to fabricate laminates. However, it is difficult to fabricate Ni/Al/Ni laminates with high interfacial shear strength and ductility if the stand-off distance has not been optimized during the explosion process. The goal of this study was to investigate the effect of stand-off distance on the microstructure and mechanical properties of Ni/Al/Ni laminates, and SEM and EDS were used to characterize the morphology and element distribution of the double layer interface. Tensile and tensile-shear tests were conducted to evaluate the mechanical properties of the laminates. The results indicated that with the increase in stand-off distance, three different kinds of interface were obtained (straight, wavy and continuously melted). Thickness of atomic diffusion layer increased with the increase in stand-off distance. Moreover, the Ni/Al/Ni laminates with wavy interface possessed highest value of ductility and interfacial bonding strength. [ABSTRACT FROM AUTHOR]

This study explores the effects of heat treatment on the microstructure and mechanical properties of explosively welded Ck60 steel/St37 steel. The objective is to find an economical way for manufacturing bimetallic plates that can be used in the rolling stand of hot rolling mill units. The explosive ratio and stand-off distance are set at 1.7 and 1.5 t ( t = flyer thickness), respectively. Since explosive welding is accompanied by such undesirable metallurgical effects as remarkable hardening, severe plastic deformation, and even formation of local melted zones near the interface, heat treatment is required to overcome or alleviate these adverse effects. For this purpose, the composites are subjected to heat treatment in a temperature range of 600-700 °C at a rate of 90 °C/h for 1 h. Results demonstrate well-bonded composite plates with a wavy interface. In the as-welded case, vortex zones are formed along the interface; however, they are transformed into fine grains upon heat treatment. Microhardness is also observed to be maximum near the interface in the welded case before it decreases with increasing temperature. Shear strength is the highest in the as-welded specimen, which later decreases as a result of heat treatment. Moreover, the energy absorbed by the heat-treated specimens is observed to increase with increasing temperature so that the lowest value of absorbed energy belongs to the as-welded specimen. Finally, fractography is carried out using the scanning electron microscope to examine the specimens subjected to shear and impact tests. As a result of heat treatment, fracture surfaces exhibit dimpled ruptures and fail in the mixed mode, while failure in the as-welded specimens predominantly occurs in the brittle mode. [ABSTRACT FROM AUTHOR]

The objective of the article is to study the development and characterization of composite coatings using nickel-tungsten carbide (Ni-WC), nickel-silicon carbide (Ni-SiC), nickel-carbon black (Ni-CB), and nickel-carbon nanotube (Ni-CNT) materials using electrocodeposition technique by varying the composition of reinforcements. The electrochemical parameters such as current density, bath temperature, and pH of the solution were maintained at constant levels for all the coating configurations. The composition of the coating and its proportion were studied using x-ray diffraction and energy dispersive x-ray spectroscopy, respectively. Mechanical properties such as ultimate tensile strength and microhardness were studied. Morphology of the coatings and fracture surfaces were studied using scanning electron microscope. Improvement in mechanical properties of composite coatings was found due to the reduction in crystalline size of the composites coatings. Although loading of carbon nanotube was the least, it also shows good mechanical properties along with Ni-WC composite coatings. [ABSTRACT FROM AUTHOR]

ZM6 magnesium alloy was prepared by solid recycling process. Effect of heat treatment on microstructure and mechanical properties of the alloy was investigated. Cold pressing was employed to prepare extrusion billets of ZM6 chips, then the billets were hot extruded at 773 K with an extrusion ratio of 25:1. During hot extrusion, the grains refined and the particles were broken. The peak-aging materials showed fine plate-shaped β′ precipitates. The ultimate tensile strength and elongation to failure of as-extruded rods was 232.2 MPa and 23%, respectively. After T5 and T6 heat-treatment, obvious improvement of the tensile strength was obtained because of dispersive particles or fine precipitates. The morphology of the fracture surfaces was examined by employing scanning electron microscope. [ABSTRACT FROM AUTHOR]

In the present study, Cu-1.8 wt.% Ni (nickel coating) composite was produced by the combination of two methods, including accumulative roll bonding (ARB) and electroplating processes. Electroplating process was done on copper strips in order to produce a nickel-particle-reinforced composite. Microstructure, texture, and the mechanical properties of the produced composite were evaluated during various cycles of ARB using optical and scanning electron microscopes, x-ray diffraction, microhardness, and tensile tests. In addition, the results were compared with Cu-Cu and also Cu-Ni (nickel sheet) samples. It was found that nickel layers were fractured from the first cycle of the process, and nickel fragments were distributed in the copper matrix as the number of cycles was increased. Variation of orientation density of α-, β-, and τ-fibers for the produced composite was examined in different cycles. Microhardness for different elements in different cycles of Cu-Ni was also evaluated. Also, the investigation of the mechanical properties showed that by proceeding the ARB process, the tensile strength of the produced Cu-Ni and Cu-Cu samples was increased. However, improvement in the mechanical properties of composite samples was more noticeable due to the reinforcing effect of nickel particles. The elongation of composite samples showed a decrease in the primary cycles, unlike Cu-Cu ones; however, it was then increased. Finally, by using scanning electron microscopy, the fracture surfaces of Cu-Ni composite were studied to disclose the fracture mechanism of the samples. [ABSTRACT FROM AUTHOR]

Acicular ferrite (AF) can significantly improve the mechanical properties of steel welds. One practical approach to enhance the formation of AF is to provide the heterogonous nucleation sites such as Ti oxides. In this study, Ti was added to different conventional welding processes including shield metal arc welding (SMAW), submerged arc welding (SAW) and tandem SAW (T-SAW). In the SMAW process, TiO2 particles as a source of Ti were inserted into the weld groove, while in the SAW and the T-SAW processes, the Ti-enriched S2MoTB wire was used as the filler metal. The microstructural evolution of weldments was characterized by employing optical and scanning electron microscopes. In addition, microhardness (Vickers, HV), Charpy impact and tensile tests were carried out to investigate the mechanical properties of weldments. Although the microhardness measurements of all weldments did not vary significantly and were in the range of 205-252 HV, there was a considerable difference in tensile and impact properties of the SAW and the T-SAW weldments. In the SMAW process, the addition of TiO2 results in no significant enhancement in tensile and impact toughness. This can be attributed to the inhomogeneous distribution of TiO2 particles as well as the formation of large inclusions in the structure. On the other hand, Ti addition to WM increased the yield strength from 489 to 552 MPa for the SAW process, and in contrast, it decreased the impact toughness from 75 to 33 J. This detrimental effect can be related to the higher deposition of other alloying elements in the WM and the formation of more ferrite side plate phase. By applying the T-SAW process, more Ti in WM led to a higher content of AF in the microstructure and increased both yield strength and impact toughness from 528 to 595 MPa and 100 to 180 J, respectively. [ABSTRACT FROM AUTHOR]

The effect of post-weld thermal treatment has been investigated experimentally in an attempt to improve the mechanical properties of welded aluminum-alloy engine head. Welding of the locally damaged engine head is performed using two different filler metals-one is the commercial aluminum filler and the other base metal itself. Mechanical properties of the repaired engine head are analyzed before and after applying the thermal treatment in terms of measured values of micro-hardness, tensile strength, yield strength, percentage elongation at different zones of the welded samples. In order to realize the effect, microstructures of different welded samples are also observed through optical and scanning electron microscopes. Results of the present investigation show that the thermal treatment significantly improves the mechanical properties as well as microstructure of the welded region of Al-alloy engine head, especially those obtained by using the base filler metal. [ABSTRACT FROM AUTHOR]

Peening techniques like laser peening and shot peening were used to modify the surface of friction stir welded 7075-T7351 Aluminum Alloy specimens. The tensile coupons were machined such as the loading was applied in a direction perpendicular to the weld direction. The peening effects on the global and local mechanical properties through the different regions of the weld were characterized and assessed. The surface hardness levels resulting from various peening techniques were also investigated for both sides of the welds. Shot peening resulted in an increase to surface hardness levels, but no improvement was noticed on the mechanical properties. In contrast, mechanical properties were improved by laser peening when compared to the unpeened material. [ABSTRACT FROM AUTHOR]