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The inconsistencies regarding the fundamental correlation between Gd content and slip (twinning) activities of Mg alloys appeal further investigations. However, the traditional slip dislocations analysis by TEM is time-consuming, and that by SEM/EBSD cannot recognize the partial slip modes. These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix. Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix. Using this method, the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips, cross-slip, and postponed twinning activities by Gd addition is quantitatively clarified.

Twinning-detwinning (TDT) behavior in a strongly basal-textured Mg-Li alloy during two-step compression (RD)-compression (ND) process was investigated using quasi-in-situ EBSD. TDT behavior and TDT variants selection were statistically discussed with the loading path for the first time. Non-Schmid twinning behavior was observed in the first step compression, owing to the local stress fluctuations by neighboring twins; in contrast, Schmid's law well predicted the detwinning variants selection. This asymmetrical TDT behavior was first investigated to date related with the strong basal texture and loading path. Besides, with the progress of compression, Schmid factors for twinning demonstrated a decreasing tendency; however, those for detwinning during the second step displayed an abnormally increasing trend, fundamentally stemming from prior twinning behavior.

Flowability, particle size distribution and particle inner pore features for powders of Ti-6Al-4V, 316-steel, and Co-29Cr-6Mo alloys produced by plasma rotating electrode process (PREP) at various rotation speeds are analyzed by using scanning electron microscopy (SEM) and synchrotron X-ray computed tomography (CT). The results show that powder flowability is related to particle size distribution, surface morphology and dynamic friction coefficient of the alloy itself. This results in the higher powder flowability at low rotation speed than that at high rotation speed. Average particle size is roughly proportional to the square root of the reciprocal of rotation speed. In addition, particle size has an important effect on the particle porosity and the number faction of hollow powder in coarse powder is obviously larger than that in fine powder. Meanwhile, the alloy composition also plays a key role on porosity due to the various surface tension of alloys.

Corrosion behaviours in hydrofluoric acid solution and mechanical performances of Ni-16Cr-11Mo-6Fe-2Cu and Ni-30Co-16Cr-11Mo-6Fe-2Cu alloys were investigated by using a variety of methods. No precipitate is observed in the present low Mo alloys, suggesting the excellent structural stability. Co leads to grain refinement and localized microstructure after hot rolling, resulting in significant enhancement in both hardness and tensile strength. Owing to the addition of Cu, all alloys with and without hot rolling show near weight loss rates after immersion. This is ascribed to the dominant passive film of Cu, which demonstrates the superior stability among the constitute elements of alloys.

The Portevin-Le Châtelier (PLC) effect in a powder metallurgy (PM) Co-Ni-based superalloy was systematically investigated via the tensile tests at temperatures ranging from 200 to 600 °C and strain rates at 1.0 × 10−4 to 1.0 × 10−2. Both normal and inverse PLC effects were observed in the PLC regime, and the former appeared in the A and B types at a low temperature, whilst the latter appeared in the C type at an elevated temperature. Both positive and negative strain rate sensitivities (SRS) were shown in PLC regime, and SRS should be derived from same types of serrations. Based on the calculated activation energy, the substitutional atom Mo is considered to take primary responsibility for the PLC effect in present alloy.

This work proposes a novel strengthening strategy for HCP alloy by fully utilizing the strengthening roles from texture and dual-precipitates in both basal and prismatic planes. The binary Mg-7Al (at%) alloy fabricated by such a strategy exhibits a superior combination of strength and strain hardening rate in major plastic strain ranges. Unlike conventionally fixed distribution of precipitate on given lattice plane, both basal and prismatic Mg17Al12 precipitates are firstly engineered to co-exist and reinforce Mg alloy. Additionally, this work reports the presence of a new precipitate morphology with a hammer-like geometric configuration for the first time to date. Further application and extension of this novel strengthening strategy to other HCP alloys, like Ti, Zr, are also discussed.

In order to investigate the effect of aging on twin boundary (TB) strengthening in magnesium alloys, the cyclic compressions along two orthogonal directions of samples with and without intermediate aging are carried out. The results show that the grains in all Mg alloys AZ31, AZ61 and AZ91 are significantly refined by twin boundaries (TBs). The TB strengthening is strongly dependent on both alloying element content and aging. Although grain refinement by TB formation occurs in AZ31, it exhibits slight strengthening effect even after aging. In contrast, significant TB strengthening after aging is observed in Mg alloys AZ61 and AZ91 with high contents of alloying elements.

Effect of Ti addition on oxidation behavior of Ni-Cr-W alloys was systematically investigated by isothermal oxidation in air. The oxidation rate is accelerated by Ti addition, due to that Cr2O3 vacancy density is increased by Ti4+ occupies Cr3+ position, which promotes the formation of Cr2O3 scales. Ti addition induced the formation of TiO2 but inhibited the formation of Ni oxide. Ti segregated on the external Cr2O3 scales after oxidation for a period time. Besides, internal oxidation and nitridation were found in both alloys containing Ti. The depth of internal oxidation and nitridation increases with the increase of Ti content.

A novel Co-Ni-based superalloy was manufactured by powder metallurgy (PM) process. The microstructure and mechanical properties of PM alloy were analyzed in detail and compared with the corresponding casting alloy. After cold swaging to 66% and subsequent aging for 800 °C for 3 h on solution treated (ST) PM alloy, the yield strengths of PM superalloy can be doubled and tripled to be 1500 and 2265 MPa respectively, as compared with 700 MPa of ST PM alloy. In contrast, for the same casting alloy after subjected to similar treatments, their corresponding yield strengths were 1100 and 1650 MPa, respectively, which are much lower than these of PM alloy. Strengthening mechanism of both PM and casting alloys were quantitatively calculated, unmasking that the higher mechanical property of PM alloy can be mainly ascribed to the higher contribution from grain boundary and precipitation strengthening.

Improving the oxidation resistance without sacrificing the electrical conductivity of Cu is of great importance for researchers due to its widespread application. In this study, oxidation resistance of Cu-5 wt%Ag alloy under solution treatment (ST) and aging treatment (AT) were studied systematically. It has been confirmed that AT sample demonstrates considerably higher oxidation resistance than ST sample at elevated temperatures. The aging treatment enhanced the formation of a continuous Ag network along grain boundaries, which could act as a barrier for both inward diffusion of oxygen and outward diffusion of Cu along grain boundaries during oxidation.

This research was aimed at investigating the high temperature oxidation behavior of Inconel 718 superalloy fabricated by electron beam melting with the building direction of 0&deg, 55&deg, and 90&deg, deviation from the Z axis of cylindrical samples. Columnar &gamma, fcc phase with preferred crystal orientations was found in all specimens. With the temperature ranging from 700 to 1000 &deg, C, the 0&deg, sample, symbolized by the lowest grain boundary density, and largest grain size, reveals the best oxidation performance. It is concluded that the building direction has more impact on the amount of grain boundary density than crystal orientation, which determined the oxidation resistance.

Microstructure and mechanical properties of novel Ni-20Co-12Cr superalloys, with and without Nb addition, were systematically studied during long-term thermal exposure. With increased exposure time, the average diameter of the γ′ precipitates increased in both alloys in succession, this is more obviously observed in alloy containing 1 wt% Nb (1Nb). It is suggested that Nb increased the γ′ coarsening rate by accelerating the diffusion of Al and Nb in γ matrix. In addition, the γ′ phase fraction is increased by about 4% in 1Nb compared to the alloy without Nb (0Nb). The morphology of the γ′ phase changed from near-spherical to cuboidal shape during exposure in both alloys. Due to the increased γ/γ′ lattice misfit by Nb addition, 1Nb alloy showed an earlier tendency of shape change. Vickers hardness results revealed that the overall hardness decreased with the exposure time because the size increment of the γ′ precipitate weakened the precipitates strengthening and Orowan strengthening.

The roles of Co on the strain-hardening behavior, deformation mechanism, mechanical properties and facture mode of Ni–16Cr–11Mo–2Cu alloy were thoroughly investigated using tensile tests, SEM, EBSD, TEM and HRTEM. Two alloys with a similar sole FCC-γ phase constitution, near grain size only except the composition difference of 30 wt% Co were fabricated in purpose. Co addition can overcome the strength-ductility trade-off by enhancing the strain-hardening rate and capacity. The deformation behavior evolves from slip-dominated to SFs-dominated after Co addition, due to significant decrease of stacking fault energy, the critical stresses for both SFs and twinning by Co addition. In terms of facture mode, dimples-dominated ductile fracture is transformed to quasi-cleavage fracture composed of cleavage planes and dimples after Co addition. This is probably owing to the special role of SFs on intensifying stress/strain incompatibility phenomenon in polycrystalline alloys.