C.Y.H. Lim

Wear of TiC-coated carbide tools in dry turning

Abstract This paper examines the flank and crater wear characteristics of titanium carbide (TiC)-coated cemented carbide tool inserts during dry turning of steel workpieces. A brief review of tool wear mechanisms is presented together with new evidence showing that wear of the TiC layer on both flank and rake faces is dominated by discrete plastic deformation, which causes the coating to be worn through to the underlying carbide substrate when machining at high cutting speeds and feed rates. Wear also occurs as a result of abrasion, as well as cracking and attrition, with the latter leading to the wearing through of the coating on the rake face under low speed conditions. When moderate speeds and feeds are used, the coating remains intact throughout the duration of testing. Wear mechanism maps linking the observed wear mechanisms to machining conditions are presented for the first time. These maps demonstrate clearly that transitions from one dominant wear mechanism to another may be related to variations in measured tool wear rates. Comparisons of the present wear maps with similar maps for uncoated carbide tools show that TiC coatings dramatically expand the range of machining conditions under which acceptable rates of tool wear might be experienced. However, the extent of improvement brought about by the coatings depends strongly on the cutting conditions, with the greatest benefits being seen at higher cutting speeds and feed rates.

The performance of TiN-coated high speed steel tool inserts in turning

While it is well known that thin, hard coatings can reduce tool wear and improve tool life and productivity, there is still little consensus over the degree of advantage coated tools have over their uncoated counterparts. This paper compares the behaviour of titanium nitride- (TiN-) coated and uncoated high speed steel (HSS) tool inserts during turning. Wear maps describing the crater wear characteristics of these tools are used to show that the extent of tool wear reduction due to the coatings depends strongly on the cutting speed and feed rate. The maps also demonstrate that the benefits of TiN coatings on HSS tools may be easily realized over a wide range of machining conditions.

The effects of machining conditions on the flank wear of TiN-coated high speed steel tool inserts

Abstract This paper explores the effects different machining conditions can have on the flank wear characteristics of TiN-coated high speed steel (HSS) tool inserts during dry turning. It is found that the extent of reduction in the measured wear rates depends strongly on the conditions of machining. Three major dominant wear mechanisms for TiN-coated HSS inserts have been identified; they are micro-abrasion, micro-abrasion and attrition, and edge chipping. The transition from one dominant mechanism to another is found to be more sensitive to cutting speed than to feed rate. Wear maps showing how wear rates and wear mechanisms vary with machining conditions have been constructed. They are useful in explaining some of the wear behaviour reported for TiN-coated HSS tools, and they provide an insight into how these coated tools may be better used to increase productivity.

Overpoling-induced property degradation in Pb(Mg1∕3Nb2∕3)O3–PbTiO3 single crystals of near-morphotropic phase boundary compositions

Overpoling phenomenon has been observed in flux-grown Pb(Mg1∕3Nb2∕3)O3–(31–32)%PbTiO3 single crystals when poled above 0.4kV∕mm at room temperature. This leads to increased property variations at intermediate poling fields (0.6–0.8kV∕mm) and to the degradation of piezoelectric properties at high poling fields (⩾1.0kV∕mm). In comparison, both PMN–28%PT and PMN–30%PT crystal compositions are resistant to overpoling, of which PMN–30%PT exhibits superior dielectric and piezoelectric properties with KT≈7500–9000, d33≈2200–2500pC∕N, and d31≈1100–1400pC∕N. The electromechanical coupling factors (k33=0.90–0.94; k31=0.48–0.55, and kt=0.58–0.62) are relatively insensitive to the poling field and crystal composition.

Mesoscopic modeling of cancer photothermal therapy using single-walled carbon nanotubes and near infrared radiation: insights through an off-lattice Monte Carlo approach

Single-walled carbon nanotubes (SWNTs) are promising heating agents in cancer photothermal therapy when under near infrared radiation, yet few efforts have been focused on the quantitative understanding of the photothermal energy conversion in biological systems. In this article, a mesoscopic study that takes into account SWNT morphologies (diameter and aspect ratio) and dispersions (orientation and concentration), as well as thermal boundary resistance, is performed by means of an off-lattice Monte Carlo simulation. Results indicate that SWNTs with orientation perpendicular to the laser, smaller diameter and better dispersion have higher heating efficiency in cancer photothermal therapy. Thermal boundary resistances greatly inhibit thermal energy transfer away from SWNTs, thereby affecting their heating efficiency. Through appropriate interfacial modification around SWNTs, compared to the surrounding healthy tissue, a higher temperature of the cancer cell can be achieved, resulting in more effective cancer photothermal therapy. These findings promise to bridge the gap between macroscopic and microscopic computational studies of cancer photothermal therapy.

The effects of work material on tool wear

Wear maps showing the wear behaviour of titanium carbide (TiC)-coated cemented carbide tools during dry turning of various types of steel have been presented in earlier studies. The maps have demonstrated that tool wear rates vary with cutting speeds and feed rates used. They have also shown that there is a range of cutting conditions, called the safety zone, within which tool wear rates are the lowest. This paper further examines, using the wear mapping methodology, the effects of different grades of steel workpieces on the wear of TiC-coated carbide tools. Wear maps constructed for the machining of AISI 1045 and 4340 steels show that flank wear is generally more severe when machining the AISI 4340 grade, especially at high cutting speeds and feed rates. Nevertheless, the contour and location of the safety zone on the wear maps for both grades of steels correspond to that revealed in previous work on general steel grades.

Effective use of coated tools — the wear-map approach

One primary motivation to use coated tool inserts instead of uncoated ones is their much-improved resistance to wear during machining, resulting in an increase in tool life. A whole host of techniques has already been developed to deposit different types of coatings onto different types of inserts. These have yielded coated inserts with a variety of performance characteristics at a range of costs. In this paper, a summary is first presented of work carried out with the aim of understanding the global wear characteristics of cutting tools; the tools used in the investigations ranged from uncoated high-speed-steel and carbide tools to selected coated inserts. From these studies, it was found that machining conditions (feed rate and cutting speed) played a critical role in determining the extent of wear on these cutting tools, whether or not they were coated. It was also found that the extent of tool wear and its relationship to the machining conditions could be readily appreciated through specially constructed wear maps. It is suggested that coated inserts could be employed in a more cost-effective manner when the machining conditions are determined based on the wear maps developed for these tools.

Synthesis and wear characterization of Al based, free standing functionally graded materials: effects of different matrix compositions

Abstract In the present study, the effects of different matrix compositions, namely, Al, Al–3.35 wt.% Cu and Al–4.08 wt.% Mg, on the resulting gradient of the SiC particulates along the bulk functionally graded materials (FGMs) synthesized by the simple, cost-effective, high yield and high deposition rate gradient slurry disintegration and deposition technique is investigated. For Al/SiCp and Al–Cu/SiCp, an increase in weight percentage of SiCp along the deposition direction with an attendant increase in porosity and microhardness was observed. However, for Al–Mg/SiCp, reverse SiCp gradient was observed, with porosity and microhardness decreasing along the deposition direction. A lower overall porosity was also observed for Al–Mg/SiCp. A reduction in CTE value of the high SiCp end was observed when compared with the low SiCp end for all three ingots. The high SiCp end was also found to be more wear resistant than the low SiCp end, except for Al–Cu/SiCp. The effects of different Al matrix compositions with the microstructural development, microhardness and wear results are correlated.

Work material and the effectiveness of coated tools

Earlier studies have suggested through the use of wear maps, that significant benefits of coated tools (in terms of lower tool wear rates) may only be realized when the appropriate machining conditions (cutting speed and speed rate) are chosen. This paper investigates the effects of work material on the wear improvement of coated tools by comparing uncoated and titanium carbide (TiC)-coated cemented carbide tools when cutting two medium steel grades: AISI 1045; and AISI 4340. Wear maps constructed for these tool-work combinations show that the TiC coating is more effective when machining the softer plain carbon 1045 grade, decreasing tool wear rates by half an order of magnitude or more over a wide range of cutting conditions. More modest reductions are achieved with the harder 4340 alloy. Nonetheless, with both steel grades, the TiC coating still significantly expands the range of machining conditions under which acceptable levels of tool wear are obtained.

Synthesis and characterization of hybrid aluminum composites reinforced with Ni particulates and interconnected Fe mesh

In this study, pure aluminum reinforced with interconnected galvanized iron mesh and Ni particulates was synthesized using an innovative disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of composite samples showed uniform distribution of Ni and Al-Ni based intermetallic particulates in the matrix material, good interfacial integrity of aluminum matrix with iron mesh and Ni particulates and the presence of minimal porosity. Results of thermal mechanical analysis indicate a decrease in the average coefficient of thermal expansion of the aluminum matrix with the use of hybrid reinforcements. Mechanical characterization also revealed that the coupled use of galvanized iron mesh and Ni particulates lead to an improvement in the hardness, dynamic modulus, 0.2% yield strength and UTS but ductility was adversely affected. An attempt is made to correlate the use of hybrid reinforcements with the improved properties exhibited by the synthesized composites.