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Metal Cutting Principles

Synergistic effect of surface textures and DLC coatings for enhancing friction and wear performances of Si3N4/TiC ceramic

The effects of ultrafine WC content on the microstructure, mechanical properties and wear resistance of regenerated coarse grained WC-10Co cemented carbides have been investigated by SEM, mechanical property tests and wear test. The results show that with the increase of ultrafine WC content, the average grain size of the regenerated cemented carbides increases first and then decreases. When the ultrafine WC content is 10%, the average grain size of the regenerated cemented carbides is the maximum (4.06 μm). Meanwhile, the irregular shape grain decreases and the growth of grain is improved. When the ultrafine WC content is 10%, the regenerated cemented carbides have the highest density (99.84%), which could alleviate the negative impact of coarse grains on hardness. The transverse rupture strength and fracture toughness of regenerated cemented carbides increases on account of crack deflection, crack branching, crack bridging, the increase of transgranular fracture of WC and dimple fracture of Co phase (TRS: 2520 MPa, KIC: 20.28 MPa·m1/2). Therefore, when the ultrafine WC content is 10%, the regenerated cemented carbides have more optimal mechanical properties. The addition of ultrafine WC particles balances the hardness and fracture toughness of the regenerated cemented carbides in the sliding wear experiment, which is found that the friction coefficient, wear rate, wear scar width and depth of regenerated cemented carbides are the smallest when the content of ultrafine WC is 15%.

Effect of ultrafine WC contents on the microstructures, mechanical properties and wear resistances of regenerated coarse grained WC-10Co cemented carbides

A roller tip was utilized in a set of self-fabricated ultrasonic burnishing equipment. Ultrasonic roller burnishing with/without heat treatment was proposed and investigated in the surface strengthening of TC11 titanium alloy material. Experimental research together with finite element analysis were carried out to perform the study. Three treatments, including conventional turning, ultrasonic roller burnishing at ambient temperature (URB) and ultrasonic roller burnishing at medium temperature (URB/HT), were comparatively evaluated in term of surface integrity and corrosion resistance of the treated sample. As a result, compared with URB, the surface of TC11 alloy treated by URB/HT had better surface finishing, which significantly improved corrosion resistance, and thus the surface of TC11 alloy was strengthened. The good performance of URB/HT was attributed to the combined effect of the high frequency dynamic impact from URB and the thermoplastic effect of the heat treatment. Owing to the excitation of the ultrasonic vibration during URB, an oscillating stress wave formed and propagated deep inside the being treated material, and the heat treatment in URB/HT case was supposed to accelerate this sort of stress propagation. Meanwhile, both the heat treatment and the dynamic oscillating stress wave facilitated the deformation of the surface layer.

Surface characteristics and corrosion behavior of TC11 titanium alloy strengthened by ultrasonic roller burnishing at room and medium temperature

Diamond-like carbon (DLC)-coated tools are suitable for the machining of various aluminum alloys, graphite, and other non-ferrous metals. The shortcomings of DLC-coated tools such as high internal residual stress, low toughness, and poor adhesion strength limit their application. In order to reveal the mechanical and cutting performance of DLC-coated tools, a DLC monolayer coating, Cr/CrN/DLC composite coating, and Cr/W-DLC/DLC composite coating had been prepared on the cemented carbide cutting tools. The influences of transition interlayer on the microstructure and mechanical properties of DLC coatings were analyzed. Tool lives, wear mechanism, and machined surface roughness obtained with uncoated cemented carbide tool, DLC monolayer–coated tool, and Cr/x/DLC-coated tool during the machining of Al-Si alloys were investigated. Compared with DLC monolayer coating, the strength ratio (ID/IG) of the DLC composite coatings with Cr/x transition structure was improved, while the sp3 covalent bond contents was decreased. The results show that the adhesion strength and toughness of the Cr/x/DLC composite coating were enhanced, and the residual stress was greatly reduced. The cutting tests further indicate that the DLC coating significantly improved the tool life. Based on comprehensive evaluation, the Cr/W-DLC/DLC composite coating has the highest adhesion, highest toughness, the lowest residual stress, and the longest tool life, and it is suitable for the machining of non-ferrous metal.

Mechanical and cutting performance of cemented carbide tools with Cr/x/DLC composite coatings

Since Dr. Carl Salomon proposed the well-known hypothesis on cutting temperatures in 1931, the debate on the hypothesis has never stopped. It shows that evolutions of temperatures with the increase of cutting speed measured at different points are different. From the tool wear and surface integrity point of view, this paper focuses on the evolutions of chip temperature (Chip temp.), tool-chip contact temperature (T-C temp.), and tool-workpiece contact temperature (T-W temp.) with the increase of cutting speed from low (100 m/min) to very high (7000 m/min). First, the cutting heat generation and the temperature increment in machining are theoretically analyzed. Then the influences of chip shape and mechanical property variations with the increase of cutting speed on the temperatures are analyzed. Finally, the cutting temperatures are semiquantitatively derived from chip colors and other heat characteristics in the chip and cutting tool obtained in cutting experiments: evolutions of Chip temp., T-C temp., and T-W temp. with the increase of cutting speed are presented based on the experiment results. The influence of chip shape and temperature variation on tool wear are also discussed.

On cutting temperatures in high and ultrahigh-speed machining

Burnishing has been proved to be a faster, lower-cost, and more effective strengthening process to improve surface integrity especially for alloy components when compared with heat treatment. It has been suggested that smaller static force is necessary to the required deformation when vibration excitation is superimposed to the static force, and this kind of material softening phenomenon resulting from external excited vibration is called acoustoplastic effect. This work is to investigate the influence of vibration excitation on the material under deformation in terms of stress condition. A 3D finite element model has been developed and validated by the experimental data. The effect of vibration frequency of 0–28 kHz on the total contact force as well as the distribution of residual stress and plastic strain fields was comprehensively analyzed. The vibrations at different frequencies studied in this work caused the increase of the maximum contact force. Overall, vibrations at 0 kHz, 0.1 kHz, 1.3 kHz, and 14 kHz led to the increases of the maximum residual stress and equivalent plastic strain while not exerting pronounced effect on the distribution of stress and strain fields of treated samples. However, in case of a very high frequency vibration at 28 kHz, pulse hammering contact force produced between the rolling ball and being treated surface, resulting in a significant change of the distribution of stress and strain fields. The observations at high vibration frequency can be interpreted as that pulse hammering contact force produced at some high frequency coupled with other process parameters caused the formation and continuous propagation of dynamic oscillatory stress wave traveling long distance inside the material.

Guosheng Su

Papers

Effect of ultrafine WC contents on the microstructures, mechanical properties and wear resistances of regenerated coarse grained WC-10Co cemented carbides

Surface characteristics and corrosion behavior of TC11 titanium alloy strengthened by ultrasonic roller burnishing at room and medium temperature

Mechanical and cutting performance of cemented carbide tools with Cr/x/DLC composite coatings

On cutting temperatures in high and ultrahigh-speed machining

An investigation of stress condition in vibration-assisted burnishing