Concentrated solar energy used for heat treatment of Ti6Al4V alloy manufactured by selective laser melting

Ti6Al4V alloy manufactured by Selective Laser Melting (SLM) technology was heat treated for the first time in solar furnaces on Plataforma Solar de Almeria, Spain. This paper focuses on demonstrating feasibility of using Concentrated Solar Energy (CSE) to heat treatment of the Ti6Al4V alloy produced by SLM as a new approach of heat treatment and an alternative to conventional techniques. SLM process is characterized by a local high heating followed by fast solidification and rapid cooling, resulting in a microstructure consisting of a fine martensite called alpha' phase. Long columnar original beta grains, with the inside original alpha' microstructure, were found in the as-fabricated SLM Ti6Al4V. Specimens were heat treated both in the horizontal (SF40) and vertical (SF5) furnace using CSE, below and above the beta-transus, under argon atmosphere and a heating rate of 60 degrees C/min. Heat treatments below beta-transus led to transformation the a' initial microstructure into a mixture of a and beta, but after some treatments the initial characteristics of the microstructure were maintained and the columnar prior beta grains remained visible in the cross section of the specimens. Treatments above beta-transus transformed the original alpha' microstructure into a lamellar alpha + beta one and they also led to formation of a colonies. Specimens have a slight weight gain after heat treatment due to contamination of SLM Ti6Al4V during heat treatment and alpha case formation. Specimens subjected to heat treatments at high temperatures close to beta-transus (850 degrees C) and above beta-transus (1015 degrees C and 1050 degrees C) have the highest variation in weight. After heat treatments, micro hardness of the most specimens was slightly decreased comparing with the microhardness of as-fabricated specimens. Dispersion of microhardness values of the heat treated specimens is greater than the as-fabricated SLM Ti6Al4V.