Laser-directed energy deposition (L-DED) is a key enabling technology for the repair of high-value aerospace components, as damaged regions can be removed and replaced with additively deposited material. While L-DED repair improves strength and fatigue performance compared to conventional subtractive techniques, mechanical performance can be limited by process-related defects. To assess the role of oxygen on defect formation, local and chamber-based shielding methods were applied in the repair of 300M high strength steel. Oxidation between layers for locally shielded specimens is confirmed to cause large gas pores which have deleterious effects on fatigue life. Such pores are eliminated for chamber shielded specimens, resulting in an increased ductility of ∼15%, compared to ∼11% with chamber shielding. Despite this, unmelted powder defects are not affected by oxygen content and are found in both chamber- and locally shielded samples, which still have negative consequences for fatigue.

In this work, an artificial neural network model is established to understand the relationship among the tensile properties of as-printed Ti6Al4V parts, annealing parameters, and the tensile properties of annealed Ti6Al4V parts. The database was established by collecting published reports on the annealing treatment of selective laser melting (SLM) Ti6Al4V, from 2006 to 2020. Using the established model, it is possible to prescribe annealing parameters and predict properties after annealing for SLM Ti-6Al-4V parts with high confidence. The model shows high accuracy in the prediction of yield strength (YS) and ultimate tensile strength (UTS). It is found that the YS and UTS are sensitive to the annealing parameters, including temperature and holding time. The YS and UTS are also sensitive to initial YS and UTS of as-printed parts. The model suggests that an annealing process of the holding time of fewer than 4 h and the holding temperature lower than 850°C is desirable for as-printed Ti6Al4V parts to reach the YS required by the ASTM standard. By studying the collected data of microstructure and tensile properties of annealed Ti6Al4V, a new Hall-Petch relationship is proposed to correlate grain size and YS for annealed SLM Ti6Al4V parts in this work. The prediction of strain to failure shows lower accuracy compared with the predictions of YS and UTS due to the large scattering of the experimental data collected from the published reports.

The effect of SiCp on the aging behavior of the extruded SiCp/AZ91 composite fabricated by stir casting was investigated in detail. The necklace-type distribution of the particles in the cast SiCp/AZ91 composite was destroyed, and the extrusion bands consisting of SiCp and small dynamic recrystallized grains formed aligning along the extrusion direction. Addition of SiCp could accelerate the aging kinetics of the AZ91 matrix because of the overlapped particle plastic zone. The improved particle distribution and refined grains caused by the recrystallization could affect the aging behavior of the SiCp/AZ91 composite. The Mg17A112 discontinuous precipitates preferred to nucleate at the SiC/Mg interfaces and the grain boundaries within the extrusion bands and then expanded into the particle-free region. Moreover, the promoted discontinuous precipitates would suppress the continuous intragranular precipitates with respect to the unreinforced AZ91 alloy.

Tensile properties of different directions of X70 pipeline steel plate were tested, and microstructural evolutions of different zones along the transverse direction (TD) were also investigated using electron backscatter diffraction. The highest strength values (yield strength and ultimate strength) appear at TD, and the diagonal direction shows the largest uniform elongation. The elongations of the polygonal ferrite and quasi polygonal ferrite grains increase with the decrease in the distance to the fracture zone. The ratio between high-angle grain boundaries and low-angle grain boundaries in the as-received steel is about 7/3 and starts to decrease from the fillet zone to the fracture zone. The refinement of grains occurs adjacent to the fracture section with the formation of subgrains. With the increase in tensile strain, the intensities of cube and γ-fiber textures increase sharply, and the reinforcement of the (111)$\left[ {\bar{1}\bar{1}2} \right]$ component was obviously larger than the (111)$\left[ {1\bar{2}1} \right]$ component in the γ-fiber texture during tensile deformation.

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.

Microstructure evolution and tensile properties of large dimensional bulk 304 stainless steel after being rolled with different thickness reductions were characterized in detail. The results showed that the steel consisted of nano-submicro-microcrystalline austenite and nanocrystalline ferrite. Submicrocrystalline austenite was broken down with the thickness reduction, when thickness reduction was 70%, all submicrocrystalline were broken down to nanocrocrystalline, and dispersed more uniformly in the microcrystalline austenite phase in the steel, but the grain size of the nanocrystalline austenite increased to 70 nm. Tensile strength increased from 850 MPa to 965 MPa, yield strength increased from 652 MPa to 837 MPa, elongation decreased from 33% to 19%, intergranular corrosion rate decreased from 1.36 g/(m2 h) to 0.46 g/(m2 h). Strength and intergranular corrosion properties increased much. When the thickness reduction was 70%, the tensile strength, yield strength, elongation, and intergranular corrosion properties were the best in the reported value of the steel.