Microhardness and wear behaviour of polycrystalline diamond after warm laser shock processing with and without coating

Abstract

Cutting tools made of ultra-hard materials such as polycrystalline diamonds offer superior wear resistance in precision machining of Aluminium alloys. However, the wear properties of these materials are dependent on their microstructural characteristics such as grain size and binder percentage. In this context, the present paper evaluates the effects of two low-energy fibre laser processes (nanosecond pulse duration) on microstructural changes of polycrystalline diamond composites and consequently investigates wear and friction characteristics and micro hardness properties. Pockets were first achieved using a single mode SPI pulsed fibre laser (1064 nm wavelength) inducing both laser shock processing (LSP) and laser peening without coating (LPwC) and characterised using a combination of scanning electron microscopy (SEM), white light interferometry, energy dispersive X-Ray (EDX) and micro hardness analyses. The as-received and processed materials were tested on a pin-on-disc for the evaluation of their wear performance. An analytical model based on the asperities of pin and disc after wear test is proposed to predict the trend of wear performance of different laser-processed materials. LSP with vinyl and quartz at a scanning speed of 500 mm s-1 achieved a micro-hardness of 110 GPa at a depth of 632 nm. LPwC at 0.8 GW cm-2 produced hybrid microstructures which share characteristics of laser shock processing and selective laser melted structures. For laser feed speed in the region of 1000 mm s-1 , micro-indentation tests revealed an improvement of hardness from 70 GPa to 95 GPa at a depth of 670 nm for LPwC. Tribotest revealed enhanced wear performance for all laser-processed pins and reduced coefficient of friction also validated by increased material removal rate when compared to the as-received material. To the best of authors' knowledge, it is reported for the first time that an improvement of wear performance can be achieved on polycrystalline diamond through LSP and LPwC.

Laser Processing of Hard and Ultra-Hard Materials for Micro-Machining and Surface Engineering Applications

“…It needs to be optimised to the material and laser beam characteristics to cause enough energy transfer for sufficient uniform material removal with limited damage to the surface. State of the art processing of PCD and PcBN materials used feed rates ranging from 2 mm/s to 900 mm/s [ 96 , 97 ]. Vazquez et al [ 95 ] used a ns laser at three laser speeds (fluence of 11.8 J/cm 2 ), to create micro-grooves on WC-Co ( Figure 14 a).…”

Unprecedented hardness of polycrystalline diamond via laser surface engineering

“…The full range of laser parameters used for the experiments are mentioned in Table 1. The method used to machine the samples with/without coatings was replicated from previous research from Pacella et al [20]. In the process with coatings the samples to be processed were fixtured on the clamping plate, the coatings plate was placed on the main sample (only when coatings were used) and the CNC controlled motion stage was moved with feed speeds and groove pitch as indicated in Tables 1 and 2 to replicate the motion of a pulsed laser milling process.…”

“…The loading and unloading time used to investigate the hardness variation were 180 s and 20 s, respectively. The Poisson's ratio of PCD material was set as 0.07 [20]. The hardness values were used to compare the differences in the physical properties between the asreceived and the laser processed samples.…”

“…Recently fibre lasers have been used in metals, ceramics, and for the first time to apply LSPwC to PCD cutting tools [20]. A fibre laser was used to shock PCD composites in absence of medium/sacrificial coatings and in presence of sacrificial coatings of different impedances to evaluate the impact of different coatings on the mechanical and wear…”

Effect of laser texturing on the performance of ultra-hard single-point cutting tools

“…Aluminium alloys have become the most remarkably used alloys for the manufacture of aerospace components [1], in the automotive industry [2] and for machinery manufacturing [3]. In the precision machining of these alloys, cutting tools made of ultra-hard materials such as polycrystalline diamond (PCD) offer high wear resistance [4] due to their low friction coefficient, low chemical affinity, high thermal conductivity and inertness to high temperatures [5]. However, due to their low melting point [6], low hardness and high ductility [7], aluminium chips adhere strongly to the cutting tool causing early tool breakage [8].…”