Mechanical properties and microstructure of 3D-printed high Co–Ni secondary hardening steel fabricated by laser melting deposition

The mechanical properties and microstructure of the 3D-printed high Co–Ni secondary hardening steel fabricated by the laser melting deposition technique was investigated using a material testing machine and electron microscopy. A microstructure investigation revealed that the samples consist of martensite laths, fine dispersed precipitates, and reverted austenite films at the martensite lath boundaries. The precipitates are enriched with Co and Mo. Because the sample tempered at 486°C has smaller precipitates and a higher number of precipitates per unit area, it exhibits better mechanical properties than the sample tempered at 498°C. Although the 3D-printed samples have the same phase constituents as Aer Met 100 steel, the mechanical properties are slightly worse than those of the commercial wrought Aer Met 100 steel because of the presence of voids.

Effect of oxygen on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr alloy

The influence of oxygen content on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr （at%） alloy in as-cast and cold-rolled states was investigated systematically in this paper. It is found that the alloy containing oxygen element is only composed of a single β phase, while the alloy without oxygen element consisted of β and α phases. Although the grain size becomes larger, the elastic de-formation ratio, strength, and hardness of the alloy are all increased with an increase of oxygen content. The as-cast alloy has excellent plastic deformation ability, but the cold-rolled alloy containing oxygen element exhibits brittle characteristics. A conclusion can be drawn that oxy-gen element can stabilize β phase, inhibit the phase transformation from β to α , and furthermore help to increase the strength and elastic de-formation ability of the alloy. 更多

Phase evolution of binary immiscible Al-Sn film

Binary immiscible Al-Sn alloy is a very important potential anode material for lithium ion batteries.The phase stability and separation process of Al-Sn film,fabricated by magnetron co-sputtering method,was investigated by X-ray diffractometer(XRD),differential scanning calorimetry(DSC) and in situ transmission electron microscopy(TEM) and explained by Miedema theoretical model.Thermodynamic analysis reveals that the asdeposited Al-Sn film will decompose spontaneously into Al-riched areas and Sn-riched areas because of the positive mixing enthalpy.The crystallization process takes place when the Al content in the Al-riched area or Sn content in the Sn-riched area increases.Experimental results show that Al-Sn thin film is composed of an amorphous matrix and well-dispersed composite nanoparticles.Every particle contains an Al-riched area and a Sn-riched area.The Snriched area crystallizes and swallows up the Al-riched area gradually during heating through uphill diffusion of the Sn atoms.Based on the theoretical analysis and experimental results,an empirical model to explain the phase evolution process in the Al-Sn film was proposed.