In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite α′-phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of α + β for heat treatment temperatures below the critical temperature (T₀ at approximately 893 °C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T₀, because the cooling rate is relatively steep, the β-phase recrystallization transforms into a compact secondary α-phase, and a basketweave structure can be found because the primary α-phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the α-phase and the β-phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

TiC/316L stainless steel (316Lss) metal matrix composite parts have been formed using selective laser melting (SLM). In this study, we have investigated the influence of the TiC mass fraction on the microstructure evolution, microhardness, friction properties, wear properties, and corrosion resistance of the TiC/316Lss composites. The results show that the microhardness increased by the addition of the TiC mass fraction. In terms of friction and wear properties, the corrosion resistance initially increased, and then decreased. Compared with the pure 316Lss (298.3 HV0.2), the microhardness of the TiC/316Lss composites, which were formed with 2 wt% TiC, was raised to 335.2 HV0.2, which was a 12.4% increase, while the average friction coefficient was 0.123. The reason for this is that the addition of TiC can effectively refine the cell size, and as the TiC content increases, the refinement effect is more obvious. During the melting process, TiC particles act as nucleation centres, hindering the growth of crystal cells, promoting the formation of the austenite phase, and forming fine equiaxed structures, which increases the strength. However, excessive TiC particles aggravate the spheroidisation during the process of SLM, leading to increased defects, as well as a decrease in density and corrosion resistance.

This research explored a novel chemical reduction of organic aluminum for plating Al on a graphene surface. The thermodynamics of the Al plating reaction process were studied. The Al plating process consisted of two stages: the first was to prepare (C₂H₅)₃Al. In this reaction, the ΔH(enthalpy) was 10.64 kcal/mol, the ΔG(Gibbs free energy) was 19.87 kcal/mol and the ΔS(entropy) was 30.9 cal/(mol·K); this was an endothermic reaction. In the second stage, the (C₂H₅)₃Al decomposed into Al atoms, which were gradually deposited on the surface of the graphene and the Al plating formed. At 298.15 K, the ΔH was −20.21 kcal/mol, the ΔG was −54.822 kcal/mol, the ΔS was 116.08 cal/(mol·K) and the enthalpy change was negative, thus indicating an endothermic reaction.

In this paper, GH4169 alloy’s distributions of temperature and stress during the selective laser melting (SLM) process were studied. The SLM process is a dynamic process of rapid melting and solidification, and we found there were larger temperature gradients near the turning of scan direction and at the overlap of the scanning line, which produced thermal strain and stress concentration and gave rise to warping deformations. The stresses increased as the distance became further away from the melt pool. There was tensile stress in the most-forming zones, but compressive stress occurred near the melt pool area. When the parts were cooled to room temperature after the SLM process, tensile stress was concentrated around the parts’ boundaries. Residual stress along the z direction caused the warping deformations, and although there was tensile stress in the parts’ surfaces, but there was compressive stress near the substrate.

In order to improve the abrasion performance of 316Lss, make full use of its advantages and broaden its application fields, the tribological behavior of the TiC particles reinforced 316Lss composites—which were manufactured by selective laser melting (SLM)—were investigated. In this study, GCr15 bearing steel was selected as the friction material and experiments on the sliding friction and wear under different loads of 15 N, 25 N and 35 N at the sliding speeds of 60, 80 and 100 mm/min were carried out, respectively. The results show that the wear performance of the TiC/316Lss composite is higher than that of the matrix during the friction and wear experiments under all conditions and the wear rate of the TiC/316Lss composite decreases with increasing the friction rate. Similar to the wear mechanism under different loads, it changes from abrasive wear to delamination wear and severe oxidative wear. At the same time, the mechanical mixed layer formed at a high speed has a protective effect on the matrix. The reason for this phenomenon is that the mechanical properties of the TiC/316Lss composites are significantly improved due to the addition of TiC particles, the refinement of cells near the TiC particles and the formation of a large number of dislocations. In addition, due to the presence of the TiC particles, the hardness and strength of the TiC/316Lss composites are greatly improved, thus the processing hardening ability of sub-surface has been improved.

TiC/316L stainless steel composites were prepared by selective laser melting. The adhesion work, interface energy and electronic structure of the TiC/γ-Fe interfaces in TiC/316L stainless steel composites were studied to investigate the heterogeneous nucleation potential of γ-Fe grains on TiC particles by using the first principle. The degree mismatch between TiC (001) and γ-Fe (001) interface was lowest. There are four TiC (001)/γ-Fe (001) interface models with different stacking sequences (on-site and bridge-site) and different atomic arrangement sequences (C centre and Ti centre). The results show that the Fe-on-Ti centre interface had the largest work of adhesion (3.87 J/m²) and lower interfacial energy (0.04 J/m²), it was more stable, and the interfacial energy of the model was lower than that of γ-Fe/Fe melt (0.24 J/m²). Strong Fe-C covalent bonds and Fe-Ti metallic bonds were formed near the interface, which increased the interfacial strength, indicating that TiC had strong heterogeneous nucleation potency for γ-Fe.