Ti-6Al-7Nb alloy is emerging as an alternative biomedical material for replacing Ti-6Al-4V alloy used in dental implants and femoral stem prosthesis applications. In cryogenic machining using liquid nitrogen, the surface integrity characteristics of Ti-6Al-7Nb alloy significantly improved compared to dry and flood-cooled machining. This study shows that surface roughness improved in cryogenic machining by 35% and 6.6% respectively, compared with dry and flood-cooled machining. Also, the hardness in the cryogenically-machined surface layer increased, by 33.6% and 14.7%, respectively, compared to dry and flood-cooled machining, with the formation of a severe plastic deformation (SPD) layer with less volume fraction of -phase.
The topic of sustainable machining has in recent times emerged as a significant and impactful area of research focus as it directly deals with environmental health and protection, economic growth and prosperity and societal wellbeing with greater human health and safety. More specifically, sustainable machining at product, process and system levels deals with reducing negative environmental impact; offering improved energy and resource efficiency; generating minimum quantity of wastes; providing operational safety; and offering improved personal health. This paper summarizes recent efforts by the world research community in sustainable machining with a systematic approach for the analysis of machining processes that are broadly defined and classified as sustainable, beginning with dry machining, and then near-dry (also known as MQL, minimum quantity lubrication) and cryogenic machining processes. The paper also extends its analysis to hybrid mode of sustainable machining which effectively combines cryogenic and MQL machining processes for improved machining productivity, performance and sustainability. While a significant part of this paper presents a summary of recent experimental analysis, the progress being made in modeling and optimization has also been discussed in the paper. In particular, major challenges involved in model development for practical implementation, with a view to selecting optimum cutting conditions and cutting tools, are primarily discussed in the paper. The need for continued modeling efforts for achieving deployable optimized conditions for sustainable machining is highly recognized, and further research is urged in numerous fronts integrating the various convergent disciplines such as materials, mechanics, computational sciences, economics, environmental sciences, etc.
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