Electron beam melting technique is a kind of near-net shaping, environmentally friendly metal additive manufacturing technique, which can form high-performance metal parts with complex shapes. It has been widely applied in the aerospace industry, biomedical application, automobile manufacturing, and other fields. Ti-6Al-4V is the most widely researched and applied alloy in the additive manufacturing field, but its microstructure is diverse, and its mechanical properties vary greatly. In this study, the effect of process parameters on the microstructure and the resulting mechanical properties of Ti-6Al-4V alloy was researched. The results show that the yield strength of Ti-6Al-4V alloy with a bimodal microstructure is higher than those with a basketweave microstructure. Energy dispersion spectrum (EDS) line scan and area scan results show that there is no element enrichment for the specimens with the highest yield strength. A speed factor of less than 40 is a must for obtaining relatively dense Ti-6Al-4V parts built with electron beam melting. We have done basic research for the subsequent manufacturing of complex shape parts, which is helpful to promote the application of electron beam melting technology in the aerospace field.

Residual stress of engineering ceramics is one of surface integrity evaluation indexes affecting the parts’ strength properties. Rotary ultrasonic grinding machining is the most powerful machining method for engineering ceramics with better surface integrity. The residual stress field distribution is changed due to micro cracks which are inevitable in the process. A residual stress distribution model of machined surface micro crack tip has been established in the paper. And the experimental results enable us to obtain surface residual stress distribution of engineering ceramics in rotary ultrasonic grinding machining. Then, we propose an evaluation parameter called confidence stress tolerance to evaluate surface residual stress characteristic. Preliminary results indicate that surface residual stress distribution is in line with the normal distribution. Confidence stress tolerance is an effective parameter to improve the evaluation reliability. Furthermore, precision and affecting factors of confidence stress tolerance evaluation have also been investigated.

The extracted position and characterization direction of specimens have an unignorable effect on the microstructural characteristics of materials produced by electron beam melting (EBM). This study focused on the effects of extracted position and characterization direction on the microstructure, defect distribution and Vickers hardness of TA15 titanium alloy fabricated by electron beam melting. Results show that the microstructure at the bottom end of TA15 specimens is coarser and hot cracks are visible at this end. Grain morphology in longitudinal direction is columnar while that in transversal direction is chessboard-like. The results of defect analysis show that gas pores are visible in transversal direction while lack of fusion exists in longitudinal direction. The average relative density of TA15 specimens in transversal direction is higher than that in longitudinal direction. The results of energy spectrum analysis show that there is evaporation of Al during the forming process, but no elements segregation and enrichment are observed. This study provides important insights on the microstructure analysis and defect evaluation of materials made by EBM technology.

Ti-5Al-4Sn-2Zr-1Mo-0.25Si-1Nb (TA32) titanium alloy is a kind of near α high temperature titanium alloy with great application prospects in aero-engine afterburners and cruise missiles. However, there are still few studies on the microstructure and mechanical properties of TA32 specimens produced by selective laser melting (SLM) technology. In this study, TA32 specimens with high strength (tensile strength of 1267 MPa) and moderate ductility (elongation after fracture of 8%) were obtained by selective laser melting. The effect of laser power on the microstructure and mechanical behavior was studied and the results demonstrated that the average grain size increases with increasing laser power from 200 W to 400 W. Micro-zone composition analysis was carried out by energy dispersion spectrum (EDS), showing that the Al concentration inner grains is higher than that near grain boundaries. Fracture analysis results demonstrated that the fracture mode of SLM TA32 specimens was cleavage fracture. The tensile strength of the specimens built with a laser power of 250 W at 500 °C, 550 °C and 600 °C was measured as 869 MPa, 819 MPa and 712 MPa, respectively.