Study of interface and base metal microstructures in explosive clad joint of Ti–5Ta–1·8Nb and 304L stainless steel

Abstract

This paper presents the microstructural modification in a dissimilar joint of Ti-5Ta-1?8Nb alloy with 304L austenitic stainless steel, fabricated using explosive cladding process. The interface had a wavy nature with occasional presence of shrinkage cavities and solidified melt zones. X-ray Rietveld and electron microprobe based analysis did not reveal the presence of intermetallic phases at the weld interface within their detection limits. Evidences for the transformation of fcc to bct phases in 304L stainless steel and formation of metastable fcc phase in Ti-Ta-Nb alloy, not predicted in the phase diagram are provided. These phase transformations are understood in terms of severe plastic deformation during explosive cladding process.

Effect of alloying elements on interdiffusion phenomena in explosive clads of 304LSS/Ti–5Ta–2Nb alloy

“…This resulted in the formation of a 0 and e martensite phases in SS and metastable fcc phase in TiTaNb alloy [3]. It is essential to design post-weld heat treatments (PWHT) to obtain a uniform microstructure without residual stresses for the intended application of the joints.…”

“…The values of reaction index 'n' and growth constant 'K 0 ' in Eq. (3) are derived from the linear fit analysis of the ln(X) vs ln(t) plot, and the values are tabulated in Table 5. From the above analysis, it is evident that the reaction index for growth of the diffusion zones in the present study is close to 2.…”

“…Based on our earlier investigations on heat-treated SS/TiTaNb explosive clads, an appreciable variation in molar volume with concentration is expected at temperatures beyond 700°C [4]. Sangeeta and Aloke Paul in a recent publication [13] have laid emphasis on incorporating the effect of molar volume for accurate determination of intrinsic diffusion coefficients in V 3 Ga system and have proposed the use of Wagner's method [14], when substantial molar volume change is involved during interdiffusion. However, the above methods are applicable for simple binary systems and there is difficulty in extending the same to multicomponent and multiphase systems, where diffusion of one element affects the other diffusing species.…”

“…A study on growth kinetics of the reaction zones in Fe-Ti weldments is of technological importance since performance of these joints is decided by the temperature and time-dependent diffusional growth of the interface [2]. Earlier, in the author's laboratory, explosive cladding process was employed to join 304L austenitic stainless steel (SS) and Ti-5 wt%Ta-2 wt%Nb (TiTaNb), an a?b alloy for an important industrial application in the spent nuclear fuel reprocessing plant [3]. Subsequent diffusion annealing of the clads at temperatures in the range of 550-800°C for various durations resulted in the formation of various reaction zones at the interface due to interdiffusion of the alloying elements [4].…”

Prediction and Confirmation of Phases Formed in the Diffusion Zone of Ti-5Ta-2Nb/304L SS Explosive Clads

“…Detailed investigations on the 'as received' clads [32][33][34][35] led to the following significant observations:…”