On the heat-treatment induced evolution of residual stress and remarkable enhancement of adhesion strength of cold sprayed Ti–6Al–4V coatings

Abstract

Cold spraying is an extremely viable repair technique for high-value aerospace components made of Ti–6Al–4V alloys. However, significant residual stresses are generated in as-sprayed coatings and it is desirable to relieve such stresses as they could impact coating adherence and subsequent performance. We have used a series of post heat treatments to identify the most suitable one for stress-relieving of cold sprayed Ti–6Al–4V coatings on Ti–6Al–4V substrates. The alleviation of macroscopic residual stresses is accompanied by changes in coating microstructures, which has also been discussed. Post heat treatment particularly at 600 and 950 ​°C results in a significant increase in the interfacial bond strength compared to as-sprayed coating. Reduction in coating porosity and increased fraction of adhered powder particles to the substrate are also attributed to the increase in coating adhesion strength.

Keywords

• Cold spray
• Ti–6Al–4V
• Residual stress
• Heat treatment
• Martensite
• Adhesion strength