C. Sudha

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.

Metastable Phase Transformation in Ti-5Ta-2Nb Alloy and 304L Austenitic Stainless Steel under Explosive Cladding Conditions

Ti-5Ta-2Nb alloy was clad on 304L austenitic stainless steel (SS) using the explosive cladding process. Both Ti-5Ta-2Nb and 304L austenitic steel were severely deformed due to high pressure (in the gigapascal range) and strain rate (105/s), which are characteristics of explosive loading conditions. Consequent changes produced in the microstructure and crystal structure of both the alloys are studied using electron microscopy techniques. The microstructure of both Ti-Ta-Nb alloy and 304L steel showed evidence for the passage of the shock waves in the form of a high number density of lattice defects such as dislocations and deformation twins. In addition, both the alloys showed signatures of phase transformation under nonequilibrium conditions resulting in metastable transformation products. 304L SS showed martensitic transformation to both α′(bcc) and ε(hcp) phases. Microscopic shear bands, shear band intersections, and twin boundaries were identified as nucleation sites for the formation of strain-induced phases. Ti-Ta-Nb alloy underwent metastable phase transformation to an fcc phase, which could be associated with regions having a specific morphology.

Reverse Transformation of Deformation-Induced Phases and Associated Changes in the Microstructure of Explosively Clad Ti-5Ta-2Nb and 304L SS

Ti-5Ta-2Nb alloy was joined to 304L austenitic stainless steel by explosive cladding technique. Explosive cladding resulted in the formation of deformation-induced martensite in 304L SS and fcc phase of Ti in the Ti-5Ta-2Nb side of the joint. The stability of these metastable phases was systematically studied using high-temperature X-ray diffraction technique and transmission electron microscopy, which enabled the optimization of the temperature window for post-cladding heat treatments.