Estudo do refinamento do grão da liga Ti-6Al-4V após tratamento térmico de envelhecimento, recozimento e têmpera

Abstract

Heat treatment of titanium alloys, such as Ti-6Al-4V, is essential to adjust their mechanical and microstructural properties. Therefore, heat treatments are essential to improve the properties of titanium alloys. The present work aimed to investigate and characterize the effect of aging, annealing and tempering heat treatments on the grain refinement of the Ti6Al4V alloy. Through thermal aging, annealing and tempering treatments, the microstructure and hardness of 7 samples were analyzed. The analyzed samples were prepared for micrographic, microhardness, XRF, XRD and SEM analysis using metallographic technique after heat treatment. Their microstructures were analyzed using optical microscopy and scanning electron microscopy. The peaks and their phases were identified using the x-ray diffractometer and the microhardness using the Vickers microhardness meter. This research found a phase transition occurring above the β-transus temperature (1050°C) that resulted in two microstructures: martensite and widmanstätten, with sudden cooling and slow cooling respectively. Three more samples were heated below the β-transus temperature (550°C, 650°C and 750°C), for 2h each, and cooled to room temperature after solubilization treatment, which resulted in the bimodal microstructure. There was a considerable increase in microhardness in relation to the base sample, with a decrease occurring only in the bimodal structure from 650°C due to overaging. The results for the microstructure varied depending on the heat treatment. Different structures could be evaluated, obtaining widmanstätten, martensite and bimodal structures. It was found that the modification in the microstructure of the Ti-6Al-4V alloy influences the microhardness in a specific way for each treatment carried out.