Influence of Processing Parameters during Hot Isostatic Pressing on Properties and Microstructure of Additive Manufactured TiAl6V4

Abstract

Abstract The process chain, typical for additive laser beam powder bed fusion manufacturing of TiAl6V4 components in the aerospace industry, includes hot isostatic pressing (HIP) to reduce the initial porosity. The comparably high temperatures and pressures required by this process, are likely to affect the microstructure and thus also the material properties. Specific variations of the HIP parameters are examined by means of controlled HIP cycles. The parameter variations were kept within conventional boundaries of aeronautics specifications. Specific tests designed to more clearly point out any interdependencies and potential benefits to HIP were also conducted using parameters deviating from the conventional ones. The influence of the HIP parameters was examined using hardness measurements, tensile tests and optical microscopy. Some samples were also examined under a scanning electron microscope. The examinations show that, especially as HIP temperatures rise, the α-lamellae in typical microstructures created by this manufacturing process will grow, reducing strength and simultaneously increasing ductility. It could also be shown that average cooling rates of 75–3000 K/h did not measurably change the microstructure or static properties. As opposed to this, specific quenching at rates of 18 000 K/h during hot isostatic pressing and subsequent ageing for 20 h at 500 °C will create secondary structures comprising α-needles of < 100 nm width. The resultant local microstructure is significantly finer and will increase strength without decreasing ductility.