The effect of explosive treatment on the formation of nitrides in Ti-6Al-4V alloy

Abstract

As-received(A-R) Ti-6Al-4V was explosively welded to 304 stainless steel and, so called, explosively treated (E-T) Ti-6Al-4V specimens were nitride ion treated in a direct current (d.c.) plasma system. The effect of shock waves on the formation of nitrides on the titanium alloys was the aim of the investigation. An effective nitration was achieved due to the high dislocation density and vacancy concentration that emanated from the shock wave exposure of explosive treatment which, in turn, accelerated diffusion of nitrogen into the titanium matrix. Nitrogen treated Ti-6Al-4V developed a surface layer of TiN (delta) followed by a Ti2N (epsilon) and interstitial nitrogen containing diffusion layer of alpha-titanium. The formation of nitrides was more effective in E-T samples when compared with A-R ones. Depending on the ion nitration temperature, from 973 K to 1173 K, high Knoop hardness values, between 800-2520, were obtained in E-T samples. These hardness values were found greater when compared with A-R samples. In E-T samples XRD results also showed VN formation, together with TiN and Ti2N nitrides. Explosively treating and subsequent nitration of Ti-6Al-4V provides an excellent opportunity for using titanium alloys in advanced structural applications without the expense of their monolithic counterparts.