Effects of Zr/(Zr+Ti) Molar Ratio on the Phase Structure and Hardness of TixZr1−xN Films

TixZr1−xN hard films with Zr/(Zr+Ti) molar ratios from 20% to 80% were prepared by multi-arc ion plating using any two of elemental Ti, elemental Zr, and TiZr alloy targets. The as-deposited TixZr1−xN films displayed similar surface and fracture cross-section morphologies and thicknesses. The effects of Zr/(Zr+Ti) molar ratio on the phase composition, preferred growth orientation, and hardness of the films were discussed. The results showed that the as-deposited films had a face-centered cubic structure and exhibited the typical characteristics of substitutional solid solutions. The lattice constant of the films increased monotonically with increasing Zr/(Zr+Ti) molar ratio. Two preferred growth orientations, corresponding to the two hardness peak values, occurred symmetrically at Zr/Ti molar ratios of 40:60 and 60:40. An inflection point with a small reduction in hardness was observed at the Zr/Ti molar ratio of 50:50.

Mechanical Properties of 316 Stainless Steel Structure produced by Pulsed Micro-plasma Additive Manufacturing

An innovative pulsed micro-plasma additive manufacturing (AM) system is proposed for the fabrication of thin-walled 316 stainless steel parts. During the deposition process, the heat accumulation from the micro-plasma can be controlled effectively by adjusting the following parameters: the AM current, pulse length of the plasma arc, and scanning speed. The width of the pool can reach 3.0 mm. The microstructural analysis, micro-hardness tests, and tensile strength tests were performed. The results of the structural characterisation showed that columnar dendrites predominated in the microstructure of thin-walled elements and exhibited epitaxial growth from the bottom to the top and from the middle to both sides, while the top grains had more variations in growth orientation. The grains had a core-shell structure with a growth orientation along the < 100 > direction of the austenite structure, and the boundary was composed of migrated C and Cr. The micro-hardness of the thin-walled structure (240–320 Hv0.3) decreased with increasing the deposition thickness. The tensile strength and yield strength of the thin-walled parts were 669 and 475 MPa, respectively. The fracture mechanism was that cracks formed along the pores along the pores of the grain boundary and then propagated along them, ultimately leading to the fracture.

Effect of Heat Treatment on Microstructures and Mechanical Properties of SS316L by Micro Selective Laser Melting

Recently, micro selective laser melting (μSLM) system equipped with finer laser beam has been developed to improve additive manufacturing resolution. The microstructures and properties of μSLM produced metals and alloys could be different from those by conventional-size SLM, which warrants further investigation. Moreover, the widely used material, SS316L stainless steel, demonstrates unique cellular structures and excellent combination of strength and ductility after SLM. How the microstructures evolve after heat treatment and affect the mechanical properties remain to be clarified for μSLMed SS316L. In this study, the effect of heat treatment on the microstructures and mechanical properties of μSLMed SS316L was studied. Two heat treatment methods, namely HT650°C-2h and HT950°C-2h, were employed. It is found that the heat treatment has no effect on phase formation, and a preferred grain growth orientation with (110) plane along building direction and a single austenite phase was detected in all samples. Cellular structures were observed in as-printed samples and found to grow up a little bit after HT650°C-2h, but disappear after HT950°C-2h. Besides, more carbides are detected after HT650°C-2h, while they are partially dissolved after HT950°C-2h. For mechanical properties, the as-printed sample shows the best combination of strength and ductility, thanks to the strengthening effects from cellular structures and dislocations. The inferior mechanical properties after heat treatment is attributed to reduction of dislocations and disappearance of cellular structures. In addition, the presence of carbides can significantly reduce the ductility.

Influence of Artificially Macroscopical Drilling on the Crystal Growth Orientation of Single Domain SmBCO Bulk Superconductor

A large drilled single domain SmBa2Cu3O7−δ (SmBCO) bulk superconductor with a diameter of 32 mm and different hole sizes was successfully fabricated using the modified top-seeded infiltration and growth (TSIG) process. The morphology, superconducting properties, and grain boundary orientation growth of the drilled SmBCO samples were investigated. It was found that not only are the properties of the drilled sample equivalent to those of normal SmBCO bulk superconductors, but also the NdBCO seed crystal can be well controlled because of the increase in the specific surface area in the solid phase pellet. In addition, the growth orientation along the tangent direction of the holes was first noticed in the drilled single domain SmBCO bulk superconductor. This conclusion is highly important for the accurate control of the growth temperature of high temperature bulk superconductors.