Machining of titanium alloys using phosphonium-based halogen-free ionic liquid as lubricant additives

Abstract

Purpose Nowadays, ionic liquids (ILs) are used as lubricant additives because of their ability to improve tribological characteristics. However, majority of the ILs contains halogen-based anions. They are extremely sensitive to moisture and produce detrimental halides and halogen acids when reacted with moisture and water. These halides and halogen acids are harmful to the health and environment of the operator’s. This paper aims to study four different lubricants including two halogen-based ILs blended in canola oil and two phosphonium-based halogen-free ILs blended in canola oil and in pure canola oil. Design/methodology/approach Viscosity and contact angle were measured by using rheometer and contact angle goniometer, respectively. Machining experiments were performed using turning centre with four different lubricants at two different cutting speeds and temperatures, and the machining forces, tool morphology and roughness of the machined surface were analysed. Findings The results showed that the inclusion of 1% phosphonium-based halogen-free ILs blended in canola oil increased the viscosity by 44.8% and reduced the cutting and thrust force by 21.7% and 26.8%, respectively, compared to pure canola oil lubricant. Microscopic analysis of tool showed lower adhesive and abrasive wear when machined with phosphonium-based halogen-free ILs blended in canola oil. The workpiece surface roughness reduced by 32% for phosphonium-based halogen-free ILs blended in canola oil compared with pure canola oil. Originality/value Halogen-free ILs are possible green lubricants, as they do not contain harmful elements such as F, S, B and Cl like halogen-based ILs. To the best of the authors’ knowledge, this is presumably the first work which shows machining performance of halogen-free ILs as lubricant additives.

Tribological performance of phosphonium-based halogen-free ionic liquids as lubricant additives

“…These halogen-free ionic liquids are non-toxic, non-corrosive and more environmentally benign alternatives to halogen-based ionic liquids for tribological applications. 33, 34…”

“…These halogen-free ionic liquids are non-toxic, non-corrosive and more environmentally benign alternatives to halogenbased ionic liquids for tribological applications. 33,34 In this work, two halogen-based ionic liquids (1-methyl 3-butylimidazolium tetrafluoroborate [BMIM BF 4 ] and 1-methyl 3-butylimidazolium hexafluorophosphate [BMIM PF 6 ]) and one halogen-free ionic liquids (trihexyl tetradecyl phosphonium bis (24,4-trimethylpentyl) phosphinate P6,6,6,14 [ i (C8) 2 PO 2 ]) were blended individually with canola oil to investigate their effect on tribological characteristics of a sliding pair. Dynamic viscosity and contact angle were measured.…”

Evaluation of tribological behavior of a circulation oil with ionic liquid and hybrid additives

“…Numerous theoretical and experimental studies have proved that ILs exhibit good lubricating properties when they are used as neat lubricants or additives in various types of lubricants for different friction pairs. [15][16][17][18][19][20][21][22][23][24][25][26][27] When used as neat lubricants, the interaction between ILs and metal surfaces depends on materials of friction pairs and the composition of cations and anions in ILs. 16,17 The increase in the length of alkyl chains of ILs can prevent direct metal-to-metal contact, resulting in low friction and wear.…”

“…28 The concentration of ILs in lubricants plays a significant role in determining their tribological performance. 21–27 For instance, a recent study by Kreivaitis 23 showed excellent tribological characteristics of two protic ILs when used as 1.0 wt% additives in water for different metal contacts. Singh and Sharma 24 observed that the inclusion of pyrrolidinium cation-based and hexafluoro-phosphate anion-based ILs, at a concentration of 1.0 wt%, improved the thermophysical properties and tribological performance of rice bran oil.…”

“…Singh and Sharma 24 observed that the inclusion of pyrrolidinium cation-based and hexafluoro-phosphate anion-based ILs, at a concentration of 1.0 wt%, improved the thermophysical properties and tribological performance of rice bran oil. Bambam et al 25,26 demonstrated that blending 1.0% of phosphonium-based halogen-free ILs to canola oil yielded notable enhancements in machining and tribological performances. Similarly, Kumar and Garg 27 found that the addition of a halogen-free IL at a concentration of 2.0 wt% in canola oil resulted in the lowest friction coefficient and wear.…”