The CoCrNiMox (x = 0, 0.1, and 0.2 in molar ratio) medium entropy alloys (MEAs) were fabricated by vacuum arc melting, followed by cold rolling and annealing treatments. The X-ray diffraction (XRD), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) were employed to characterize the microstructures. It has been shown that the CoCrNi MEA has a single FCC phase and the Mo-containing MEAs contain (Cr, Mo)-rich σ precipitates. In addition, the Mo addition caused significant grain refinement, due to the fact that the presence of σ phase exerts a strong pinning effect on the grain boundary migration. The hardness testing results indicate an increment in Vickers hardness from 187.5 ± 4.5 Hv of CoCrNi alloy to 309.5 ± 10.3 Hv of CoCrNiMo0.2 alloy. The yield strength and ultimate tensile strength also increase from 339 ± 2 to 644 ± 5 MPa and from 810 ± 5 to 1071 ± 17 MPa, respectively, but the elongation drops from 88.4 ± 4.0% to 29.5 ± 7.6%. The grain refinement and the precipitation of σ phase make synergistic contribution to the reinforcement of Mo-containing CoCrNi-based MEAs. The details and explanations in this study may guide the future design and research of the CoCrNi-based quaternary alloys with enhanced properties.

A Cu–3%Ti (wt%) alloy was processed by multiaxial forging (MAF) at cryogenic temperature up to 3 cycles, imposing a total strain of 1.6. Microstructure and mechanical properties of the unprocessed and cryo-forged samples were analyzed. X-ray diffraction results showed deviation in peak broadening and peak intensity of the cryo-forged samples in comparison to that of unprocessed, which are due to texture modification caused by grain refinement during the MAF process. Microstructural analysis showed reduction in grain size from 80 µm in the as-received condition to 250 nm after 3 cycles. Electron backscatter diffraction results indicated the transformation of high angle grain boundaries to low angle grain boundaries in all 3 cycles when compared to the as-received condition. Reduction in ductility was observed after 1 cycle, but with an increase in the number of cycles, both strength and ductility increased. After 3 cycles, ultimate tensile strength and hardness reached 1126 MPa and 427 Hv as compared to 528 MPa and 224 Hv for the as-received condition. Fractography analysis showed decrement in dimple size after 1 cycle, in comparison to that of the as-received condition. However, it kept on increasing for higher number of cycles.

An Al–3% B master alloy has been subjected to equal channel angular pressing (ECAP). The grain refining performance and fading resistance of an Al–3% B master alloy on a commercial purity Al (CPA) have been evaluated. The effect of the number of ECAP passes on the size and the distribution of the AlB2 particles, the grain size of CPA ingots with and without adding the Al–3% B master alloy subjected to ECAP have been investigated. The mean size of AlB2 particles was significantly reduced from ∼34 to ∼12 μm after four ECAP passes. Fine blocky AlB2 particles were uniformly distributed in the Al matrix. It has been revealed that when it was inoculated by the Al–B master alloy subjected to ECAP, the grain size of α-Al was decreased from ∼1200 to ∼180 μm after four ECAP passes, beyond that, the grain size tends to be saturated. It has been proved that grain refinement efficiency and fading resistance of the Al–3% B master alloy subjected to ECAP in CPA ingots was enhanced.

The aim of this study is to investigate the effects of different master alloys containing Ti, B, and Zr on the structure and tensile properties of thin-section A356 aluminum alloy in as-cast and T6-treated conditions. Microstructural examinations were performed using light optical and scanning electron microscopy. The results showed that the addition of 0.1 wt% Ti, 0.05 wt% B, and 0.1 wt% Zr decreases the average grain size of the cast alloy from 840 μm to 387 μm, 236 μm, and 363 μm, respectively. This structural refinement results in the variation of the α-Al primary phase distribution mode from dendritic to rosettelike. It has been found that 0.6 wt% Al–8B master alloy (0.05 wt% B) is the strongest to refine the structural parameters. This leads to the enhancement of both ultimate tensile strength and elongation values from 208 MPa and 6.2% in as-cast to 290 MPa and 12.5% in B-refined alloy at T6-treated conditions. In addition, the presence of more fine dimples on the fracture surfaces of the T6-treated specimens revealed that T6-treatment encourages ductile mode of fracture.

Accumulative roll bonding (ARB) process was used to develop Mg–6% Zn/Al and Mg–6% Zn/anodized–Al multilayered composites. Microstructural characterization was done using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattered diffraction, and transmission electron microscopy. An average grain size measured in the roll-bonded layers of Al, anodized Al, and Mg–2% Zn was found to be 1.8 μm, 1.6 μm, and 0.6 μm, respectively. Phases Al17Mg12, AlMg4Zn11, and Al2O3 after 5-pass of ARB were confirmed by X-ray diffraction analysis. The Mg–6% Zn/Al and Mg–6% Zn/anodized Al composites exhibited tensile strengths ∼252 MPa and ∼256 MPa, respectively, after a 5-pass ARB process. Hardness of the individual layers of composite increased linearly with an increase in the number of ARB passes. Fractographs of the multilayered composite illustrated the ductile failure in Al and anodized Al layers and transgranular brittle fracture in Mg–6% Zn layers.

In this study, a mesoscale dislocation simulation method was developed to study the orthogonal cutting of titanium alloy. The evolution of surface grain structure and its effects on the surface mechanical properties were studied by using two-dimensional climb assisted dislocation dynamics technology. The motions of edge dislocations such as dislocation nucleation, junction, interaction with obstacles, and grain boundaries, and annihilation were tracked. The results indicated that the machined surface has a microstructure composed of refined grains. The fine-grains bring appreciable scale effect and a mass of dislocations are piled up in the grain boundaries and persistent slip bands. In particular, dislocation climb can induce a perfect softening effect, but this effect is significantly weakened when grain size is less than 1.65 μm. In addition, a Hall–Petch type relation was predicted according to the arrangement of grain, the range of grain sizes and the distribution of dislocations.

The effect of nitrogen gas addition in Ar-based double-layer shielding gas on the impact toughness of welded ultra-ferritic stainless steel during an autogenous gas tungsten arc welding (GTAW) process was investigated. The nitrogen behavior was proposed. The microstructure, mechanical properties, and fracture surface morphology of the weld metals have been evaluated. More equiaxed crystals, refined grain, narrow HAZ width, and increased microhardness were produced with nitrogen addition. Experimental findings indicated that nitrogen diffused into HAZ and dissolved into weld pool. The solute distribution was changed thus bringing significant constitutional supercooling and decreased temperature gradient of weld pool, which contributed to fine microstructure. Impact toughness at room temperature was enhanced from 2J to 9J (welds), 5J–13J (HAZ). Ductile fracture zone was produced about 0.3–0.5 mm thickness distance from the weld surface. A significant increased impact toughness of weld metal was due to the refinement of microstructure and element addition.

A new ultrahigh strength hot rolled Ti–Mo-bearing ferritic steel was developed through chemical composition design and rolling processing optimization. To maximize the potential of nanometer-sized (Ti, Mo)C carbide in terms of strengthening ferrite matrix, the optimal chemical composition of 0.1C–0.2Ti–0.4Mo (wt%) was determined through considering the atomic ratio of elements, the solubility temperature of (Ti, Mo)C in austenite, and the excessive growth critical temperature of austenite grain during reheating. The rolling condition in the region through austenite recrystallization region to austenite nonrecrystallization region was adopted to realize a homogenous and fine ferrite grain structure. Results showed that the simulated coiling at 600 °C was found to provide an attractive combination of ferrite grain refinement hardening (360 MPa) and precipitation hardening (324 MPa). An optimal combination of strength and ductility was achieved after coiling at 600 °C (yield strength: 912 MPa; ultimate tensile strength: 971 MPa; total elongation: 16.0%). In addition, the nanometer-sized (Ti, Mo)C carbide was characterized by transmission electron microscopy (TEM) and physical–chemical phase analysis, and its role was discussed in details.

A nanostructured surface layer was formed on an Inconel 600 plate by subjecting it to surface mechanical attrition treatment at room temperature. Transmission electron microscopy and high-resolution transmission electron microscopy of the treated surface layer were carried out to reveal the underlying grain refinement mechanism. Experimental observations showed that the strain-induced nanocrystallization in the current sample occurred via formation of mechanical microtwins and subsequent interaction of the microtwins with dislocations in the surface layer. The development of high-density dislocation arrays inside the twin-matrix lamellae provides precursors for grain boundaries that subdivide the nanometer-thick lamellae into equiaxed, nanometer-sized grains with random orientations.