Investigation of Cracks Generated During Flow Forming of Nb–Hf–Ti Alloy Sheet

Niobium alloy Nb-Hf-Ti sheets are flow formed to make a conical divergent. During cold forming of the sheet, cracking was noticed on the surface. Visual observations of the cracks and microstructural and fractographic analysis revealed the presence of built-up layer and delaminations at the cracked site. Serration marks on the formed surface indicated a relatively higher feed rate. Work hardening of the material was also observed. This paper discusses the reasons for crack generation and provides the remedial measures to avoid such cracks during flow forming.