Performance Study of Cryo-Treated End Mill Via Wet, Cryogenic, and Hybrid Lubri-Coolant-Milling Induced Surface Integrity of Biocompatible Mg Alloy AZ91D

Abstract

The excellent biodegradability of the magnesium (Mg) alloys is gradually proving them as the potential substitutes to several biomedical implants such as chemotherapy ports or screws, which are required to be removed via secondary surgeries after a specific period of time. However, an early degradation of these alloys even before the complete healing of the damaged tissue, when exposed to the physiological atmosphere, has been limiting their full-fledged application. Some latest research articles suggest that such challenges can be effectively overcome by improving the surface integrity of Mg alloys using the sustainable manufacturing techniques, such as cryogenic machining. Recent literatures also report the outperformance of the cryogenically treated (cryo-treated) cutting tools for achieving an enhanced surface integrity. In this relation, the present research attempts to improve the surface integrity of one of the most commonly used biocompatible alloys of magnesium, known as AZ91D. For this reason, a TiAlN coated-cemented carbide end mill was used in an untreated and cryo-treated state amid wet, cryogenic, and hybrid-lubri-coolant-milling conditions. The milling and FESEM (field emission scanning electron microscopy) results showed a considerable improvement in the surface integrity in terms of an augmented surface roughness and microhardness at 56.52 m/min cutting speed with the cryo-treated end mill during hybrid-lubri-coolant-milling. At the high cutting speed hybrid-lubri-coolant-milling, the cryo-treated end mill attained 35.71% and 48.07% better surface finish than that of cryo and wet-lubri-coolant-milling, respectively. Although, the highest surface microhardness was achieved by the cryo-treated end mill amid cryo-lubri-coolant-milling, due to the poorest surface quality observed in terms of the maximum number of machining-induced cracks, the hybrid-lubri-coolant-milled surface was preferred over the cryo and wet-lubri-coolant-milled surfaces. Further, the FESEM and EDS (energy-dispersive X-ray spectroscopy) analyses confirmed the oxide layer produced by the cryo-treated end mill amid hybrid-lubri-coolant-milling, to be the thinnest (12.16 µm) and most uniform passivation layer.