Investigation of the effects of heat treatment and hot isostatic pressing in micro-drilling of Ti6Al4V alloy fabricated by laser powder bed fusion

• Published in: Precision engineering Vol. 91; pp. 617 - 631
• Main Authors: Balcı, Ahmet, Çiçek, Adem, Uçak, Necati, Aslantas, Kubilay
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.2024
• Subjects: Heat treatment; Hot isostatic pressing; Laser powder bed fusion; Micro-drilling; Ti6Al4V; Laser powder bed fusion; Heat treatment; Micro-drilling; Ti6Al4V; Hot isostatic pressing
• ISSN: 0141-6359
• DOI: 10.1016/j.precisioneng.2024.10.016

In this study, micro-drilling performance of laser powder bed fusion (LPBF) Ti6Al4V alloy with heat treatment (HT) and hot isostatic pressing (HIP) post-processing conditions was investigated and compared to wrought material. The tests were performed at two spindle rotational speeds (5000 and 10,000 rev/min) and a feed per tooth (4 μm/tooth) under dry and minimum quantity lubrication (MQL) conditions using conventional drilling (CD) and peck drilling (PD) strategies. Micro-drilling performance was evaluated in terms of thrust force, surface roughness, subsurface microstructure and microhardness, burr formation, and tool wear. The test results showed that LPBF-HT and LPBF-HIP Ti6Al4V alloys exhibited different micro-drilling performances than the wrought material due to their different microstructural and mechanical properties. The LPBF-HIP Ti6Al4V characterized by higher strength and lamellar microstructure with higher β phase fraction (33.2 %) led to higher thrust force, lower surface quality and higher burr height. On the other hand, the wrought Ti6Al4V with higher ductility, lower hardness, and lower β phase fraction (16.3 %) showed lower thrust forces, surface roughness, and burr height. Notably, employing MQL conditions with the PD strategy provided good surface quality and reduced burr formation. A higher degree of tool wear was obtained in micro-drilling of LPBF-HIP Ti6Al4V. The major wear types were adhesion, BUE, and flank wear. Besides, chippings were observed in micro-drilling of LPBF-HT and LPBF-HIP Ti6Al4V. •Higher thrust force, surface roughness, burr height, and tool wear were observed for LPBF-HIP Ti6Al4V.•Peck drilling strategy under MQL condition significantly improved the hole quality.•Increasing cutting speed resulted in lower thrust force and better hole quality.•The major wear types were adhesion, BUE, and flank wear.