Tribological Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuCrZr Composites

Al₂O₃ particles reinforced Cu–Cr–Zr alloy matrix composite was fabricated through a powder metallurgy plus hot extrusion process by using the water atomization Cu–Cr–Zr powder as raw material. The effect of aging treatment on the tribological behavior of the composite was investigated. Experimental results show that tiny coherent precipitated phases were formed in the matrix after proper aging treatment and therefore good combination properties could be obtained. The wear rates of the Al₂O₃/CuCrZr composite and its matrix alloy were obviously influenced by the aging treatment, wherein the best wear resistance was reached at the aging temperature corresponding to the highest Vickers hardness. The major reason was that the depth of plastic deformation in the subsurface region was dramatically decreased due to the improvement of mechanical properties of the matrix, and therefore adhesion induced surface materials loss could be markedly alleviated. By comparing with the SiC20 vol%/Cu composite, it is indicated that the Al₂O₃/CuCrZr composite exhibited much better wear resistance as well as higher electrical conductivity.     

Mechanical and tribological behavior of the metal matrix composite AA6061/ZrO<Subscript>2</Subscript>/C

This study investigates the influence of zirconium dioxide (ZrO₂) and graphite (C) on the mechanical and tribological behavior of aluminum-based metal matrix composite (AA6061) fabricated through the stir casting. Metal matrix composites (MMC) are prepared with the following weight percentages: 100 % AA; 96 % AA-2 % ZrO₂-2 % C; 88 % AA-6 % ZrO₂-6 % C; 92 % AA-6 % ZrO₂-2 % C; and 96 % AA-2 % ZrO₂-6 % C. The microstructure and the mechanical and tribological behavior are characterized, and their correlations are obtained. Microstructural studies of the MMC reveal a uniform distribution of ZrO₂ and C particles in the AA6061 matrix. The addition of ZrO₂ improves the hardness from 6 % to 12 % (30 HRC to 40.94 HRC) and the ultimate tensile strength from 8 % to 15 % (128 MPa to 166.3 MPa) of the base metal (AA6061). The tribological behavior of wear and the frictional properties of the MMC are also studied by performing dry sliding wear test using pin-on-disc method. Result shows that the minimum and maximum wear rates of MMC are 5 E-9 and 6.2 E-9 (g/mm), respectively, at speed of 850 rpm and constant sliding distance of 1000 m.     

Enhancement of wear resistance of ductile cast iron by Ni–SiC composite coating

Wear resistance of unalloyed ductile iron (Dl) can be enhanced either by heat treatment or by deposition of hard coating. The electrodeposition of Ni–SiC composite on unalloyed Dl (GGG 40) has been applied. The effect of operating conditions including current density and SiC content in the plating solution on the SiC incorporation in the deposited layer were studied. It was found that the volume percent of SiC particles in the composite layer increases with increasing current density and SiC content in the bath. The maximum SiC incorporation could be attained at optimum conditions; 60 g/1 of SiC particles in suspension, 5 A/dm², pH 5 and 50 °C. Also the results reveal that the particle inclusion in the coating layer depends mainly on the treatment process (activation with PdCI₂). The mechanical properties of the composite such as hardness and wear resistance were examined comparing with the uncoated substrate. The reinforced particles incorporated with Ni-matrix improve the hardness and wear resistance of coated Dl comparing with uncoated substrate.     

Microstructure and Tribological Properties of a HfB<Subscript>2</Subscript>-Containing Ni-Based Composite Coating Produced on a Pure Ti Substrate by Laser Cladding

A HfB₂-containing Ni-based composite coating was fabricated on Ti substrates by laser cladding, and its microstructure and tribological properties were evaluated during sliding against an AISI-52100 steel ball at different normal loads and sliding speeds. The morphologies of the worn surfaces were analyzed by scanning electron microscopy (SEM) and three-dimensional non-contact surface mapping. The results show that wear resistance of the pure Ti substrate and NiCrBSi coating greatly increased after laser cladding of the HfB₂-containing composite coating due to the formation of hard phases in the composite coating. The pure Ti substrate sliding against the AISI-52100 counterpart ball at room temperature displayed predominantly adhesive wear, abrasive wear, and severe plastic deformation, while the HfB₂-containing composite coating showed only mild abrasive wear and adhesive wear under the same conditions.     

Cutting performance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> based SiC ceramic cutting tools

Composites of Si₃N₄-SiC containing up to 30 wt% of dispersed SiC particles were fabricated via hot-pressing with an oxynitride glass. To determine the effect of sintering time and SiC content on the mechanical properties and the cutting performance, the composites with fixed 8 hr-sintering time and 20 wt% SiC content were fabricated and tested. Fracture toughness of the composites increased with increasing sintering time, while the hardness increased as the SiC content increased up to 20 wt%. The hardness of the composites was relatively independent of the grain size and the sintered density. For machining heat-treated AISI4140, the insert with 20 wt% SiC sintered for 8 hr showed the longest tool life while the insert with 20 wt% SiC sintered for 12 hr showed the longest tool life for machining gray cast iron. An effort was made to relate the mechanical properties, such as hardness, fracture toughness and wear resistance coefficient with the tool life. However, no apparent relationship was found between them. It may be stated that tool life is affected by not only the mechanical properties but also other properties such as surface roughness, density, grian size and the number of the inherent defects in the inserts.     

Wear Behaviour of In Situ Al/TiB<Subscript>2</Subscript> Composite: Influence of the Microstructural Instability

In this present work, the in situ Al (A380)/5 wt%TiB₂ composites were fabricated through salt–melt reaction using halide salts such as potassium hexafluorotitanate (K₂TiF₆) and potassium tetra fluoroborate (KBF₄) salts as precursors. The composites were produced at four different melt temperatures (700, 750, 800, 850 °C). The formation of particle was confirmed from XRD results. The wear behaviour of Al/5 wt% TiB₂ composite was investigated by varying the wear test parameters such as sliding temperature (25, 100, 150, 200 °C), applied load (10, 20, 30, 40 N), sliding velocity (0.4, 0.7, 1, 1.3 m/s). The microstructure of Al/5 wt% TiB₂ composite was correlated with the wear characteristics of the composites. The wear resistance of Al/5 wt% TiB₂ composite was significantly improved due to the presence of TiB₂ particle in Al matrix material. The composite produced at melt temperature 800 °C showed a higher wear resistance at applied load: 10 N, sliding temperature: 25 °C and sliding velocity: 0.7 m/s. The wear mechanism for each of the tested condition was identified from the worn surfaces using scanning electron microscopy (SEM). ANOVA test was carried out to find out significant factor for the wear resistance of composite. The checking of adequacy of experimental value for the wear behaviour of composite for different testing condition was analysed by residual plots using statistical software.     

Development of sheet metal forming dies with excellent mechanical properties using additive manufacturing and rapid tooling technologies

Cost and time are two major concerns that are needed to manufacture new sheet metal forming dies in the industry. A cost-effective approach for rapid production of sheet metal forming dies with excellent wear resistance and mechanical properties was developed using additive manufacturing and rapid tooling technologies. This paper deals with the effect of zirconia (ZrO₂) addition on the mechanical properties of sheet metal forming dies. Sheet metal forming experiments confirmed that the sheet metal forming dies fabricated by epoxy resin filled with 30 wt% ZrO₂ particles have the low corner wear. The sheet metal dies can be fabricated within 2 days to meet the requirements of reducing the development time in the research and development stage for a new product.     

Synergistically toughening effect of SiC whiskers and nanoparticles in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based composite ceramic cutting tool material

In recent decades, many additives with different characteristics have been applied to strengthen and toughen Al₂O₃-based ceramic cutting tool materials. Among them, SiC whiskers and SiC nanoparticles showed excellent performance in improving the material properties. While no attempts have been made to add SiC whiskers and SiC nanoparticles together into the ceramic matrix and the synergistically toughening effects of them have not been studied. An Al₂O₃-SiC_w-SiC_np advanced ceramic cutting tool material is fabricated by adding both one-dimensional SiC whiskers and zero-dimensional SiC nanoparticles into the Al₂O₃ matrix with an effective dispersing and mixing process. The composites with 25 vol% SiC whiskers and 25 vol% SiC nanoparticles alone are also investegated for comparison purposes. Results show that the Al₂O₃-SiC_w-SiC_np composite with both 20 vol% SiC whiskers and 5 vol% SiC nanoparticles additives have much improved mechanical properties. The flexural strength of Al₂O₃-SiC_w-SiC_np is 730±95 MPa and fracture toughness is 5.6±0.6 MPa·m^1/2. The toughening and strengthening mechanisms of SiC whiskers and nanoparticles are studied when they are added either individually or in combination. It is indicated that when SiC whiskers and nanoparticles are added together, the grains are further refined and homogenized, so that the microstructure and fracture mode ratio is modified. The SiC nanoparticles are found helpful to enhance the toughening effects of the SiC whiskers. The proposed research helps to enrich the types of ceramic cutting tool and is benefit to expand the application range of ceramic cutting tool.     

Tribological Property of Ni<Subscript>3</Subscript>Al Matrix Composites with Addition of BaMoO<Subscript>4</Subscript>

The Ni₃Al matrix composites with addition of 10, 15, and 20 wt% BaMoO₄ were fabricated by powder metallurgy technique, and the tribological behaviors were studied from room temperature to 800 °C. It was found that BaAl₂O₄ formed during the fabrication process. The Ni₃Al composites showed poor tribological property below 400 °C, with high friction coefficients (above 0.6) and wear rates (above 10⁻⁴ mm³/Nm). However, the composites exhibited excellent self-lubricating and anti-wear properties at higher temperatures, and the composite with addition of 15 wt% BaMoO₄ had the lowest wear rate (1.10 × 10⁻⁵ mm³/Nm) and friction coefficient (0.26). In addition, the results also indicated that BaAl₂O₄ for the Ni₃Al composites did not exhibit lubricating property from room temperature to 800 °C.     

Friction and wear properties of CN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC in water lubrication

Amorphous carbon nitride coatings (a-CN_x) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN_x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN_x/SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN_x/SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN_x/SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN_x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN_x coating was reduced by a factor up to 100~1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN_x/SiC is related to formation and transfer of easy-shear friction layer.     

HVOF-Sprayed Adaptive Low Friction NiMoAl–Ag Coating for Tribological Application from 20 to 800 °C

An adaptive NiMoAl–Ag composite coating was deposited by high-velocity oxy fuel spraying, and its tribological properties from 20 to 800 °C under unlubricated conditions were evaluated using a CSM high-temperature tribometer. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the coating and corresponding wear tracks to determine the lubrication mechanisms. The results showed that the friction coefficient of the NiMoAl–Ag composite coating was around 0.3 from 20 to 600 °C and reached the lowest value of 0.09 at 800 °C. Meanwhile, wear rates of the coating were maintained on the order of 10^?5 mm³/N m at the test temperatures except for 400 and 600 °C. Characterization of the NiMoAl–Ag coating revealed that silver provided lubrication below 400 °C. Ag₂Mo₂O₇ and Ag₂MoO₄, which were formed through tribochemical reactions, acted as high-temperature lubricants above 400 °C. It was especially proposed that silver in a nearly molten state was effective in reducing the friction of the NiMoAl–Ag coating at 800 °C. Moreover, a comprehensive lubrication mechanism model of an NiMoAl–Ag composite coating at 800 °C was established to explain the extremely low friction coefficient and wear rate of the coating.     

High Wear Resistance of Magnetron Sputtered Cr<Subscript>80</Subscript>Si<Subscript>20</Subscript>N Nanocomposite Coatings: Almost Independent of Hardness

Hardness has been popularly considered as an essential factor defining the wear resistance of hard coatings. Here, we report magnetron sputtered Cr₈₀Si₂₀N nanocomposite coatings, of widely varied packing densities, that exhibited identical specific wear rates, while the hardness changed over a wide range (from ~12 to ~36 GPa). All the Cr₈₀Si₂₀N coatings were free of extended and uninterrupted columnar boundaries, and retained low specific wear rates in the ball-on-plate sliding tests against Al₂O₃ counterpart with a normal load of 5 N (less than 3.0?×?10^?16 m³/N m under ambient condition and less than 2.0?×?10^?15 m³/N m under 3.5 wt% NaCl solution, respectively). Post examination reveals extensive interruption or termination of cracks in the wear tracks of the under-dense coatings, indicative of extrinsic toughening mechanisms by effective relief of local contact stress. Our results suggest that a critical role of toughening rather than hardening, played in enhancing the wear resistance of hard coatings, and thus would pave a way to develop highly wear-resistant coatings with a low hardness.     

Defect intelligent identification in resistance spot welding ultrasonic detection based on wavelet packet and neural network

Experimental correlation between varying processing and wear behaviour of ternary Ni-Co-SiO₂ composites coating was investigated. The parameter used in this research are: SiO₂ (5–25 wt%), thermal treatment (100–300 °C), applied load (5–15 N). The results show that novel ternary Ni-Co-SiO₂ nanoparticle composite coating was successful applied to mild steel. The addition SiO₂ nanoparticles in the coating Ni-Co bath lead to uniform microstructure. Thermal treatment of the coating at 300 °C decreased wear rate by (?0.031), increasing the wt% of SiO₂ from 0 to 25 decreased the wear rate by ?0.018, applied load increases from 5 to 15 N raises the wear rate raises (0.0097), The lower wear rate was obtained at 25 wt% SiO₂, applied load 5 N and thermal treatment at 300 °C. Validation of the results from pin on disc test with electro-hydraulic servo PV friction testing machine shows the same wear pattern. One can concluded in this work that the wear rate of the coated materials depend on the made up of the coating and not on the type of wear mechanism. It have be established in this work that thermal treatment and SiO₂ nanoparticle can be used to enhance the wear behaviour of Ni-Co coating of mild steel.     

Microstructure and performance of multi-dimensional WC-CoCr coating sprayed by HVOF

WC-based coatings deposited by high velocity oxy-fuel (HVOF) spraying have been widely used in many industrial fields, where mechanical components are subjected to severe abrasive wear. Much attention has been especially paid to nanostructured and multimodal WC-based coatings due to their excellent abrasive wear resistance. In this study, a new kind of multi-dimensional WC-10Co4Cr coating, composed of nano, submicron, micron WC particles and CoCr alloy, was developed by HVOF. The microstructure, porosity, microhardness, fracture toughness, and electrochemical properties of the coating were investigated in comparison with nanostructured WC-10Co4Cr coating deposited by HVOF. Abrasive wear resistance of both WC-10Co4Cr coatings was evaluated on wet sand rubber wheel abrasion tester. The results show that the multi-dimensional coating possesses low porosity (0.31 ± 0.09%), excellent microhardness (1126 ± 115 HV_0.3), fracture toughness (4.66 ± 0.51 MPa m^1/2), and outstanding electrochemical properties. Moreover, the multi-dimensional coating demonstrates approximately 36% wet abrasive resistance enhancement than the nanostructured coating. The superior abrasive wear resistance originates from the coating’s multi-dimensional structure and excellent mechanical and electrochemical properties.     

Effect of Fluoride Content on Friction and Wear Performance of Ni<Subscript>3</Subscript>Al Matrix High-Temperature Self-Lubricating Composites

The self-lubricating composites Ni₃Al–BaF₂–CaF₂–Ag–Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The Ni₃Al–6.2BaF₂–3.8CaF₂–12.5Ag–10Cr composite showed the best friction coefficients (0.29–0.38) and wear rates (4.2 × 10⁻⁵–2.19 × 10⁻⁴ mm³ N⁻¹ m⁻¹) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO₄ on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property.     

Tribological properties of ZrO2 (Y2O3)-Mo-BaF2/CaF2 composites at high temperatures

ZrO₂ (Y₂O₃) with different contents of BaF₂/CaF₂ and Mo were fabricated by hot pressed sintering, and the tribological behavior of the composites against SiC ceramic was investigated from room temperature to 1000 °C. It was found that the ZrO₂ (Y₂O₃)-5BaF₂/CaF₂-10Mo composite possessed excellent self-lubricating and anti-wear properties. The low friction and wear were attributed to enhanced matrix and BaMoO₄ formed on the worn surfaces.     

Cutting performance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/TiC micro-nanocomposite ceramic tool in dry machining of hardened steel

A type of Si₃N₄/TiC micro-nanocomposite ceramic cutting tool material was fabricated using Si₃N₄ micro-matrix with Si₃N₄ and TiC nanoparticles. Cutting performance of the Si₃N₄/TiC ceramic cutting tool in dry cutting of hardened steel was investigated in comparison with a commercial Sialon insert. Hard turning experiments were carried out at three different cutting speeds, namely 97, 114, and 156 m/min. Feed rate (f) and depth of cut (a _p) were fixed at 0.1 mm/rev and 0.2 mm, respectively. Results showed that cutting temperature increased rapidly to nearly 1000 °C with increasing cutting speed. The two types of cutting tools featured similar wear behavior. However, the Si₃N₄/TiC micro-nanocomposite ceramic cutting tool exhibited better wear resistance than the Sialon tool. Morphologies of crater and flank wear were observed with a scanning electron microscope. Results indicated that wear variation of the two types of ceramic cutting tools differed in the same conditions. Wear of the Si₃N₄/TiC micro-nanocomposite ceramic cutting tool is mainly dominated by abrasion and adhesion, whereas that of the Sialon ceramic cutting tool is dominated by abrasion, adhesion, thermal shock cracking, and flaking.     

Wear Behavior of Composites Based on ZA-27 Alloy Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles Under Dry Sliding Condition

In present study, the effect of Al₂O₃ particle reinforcement on the sliding behavior of ZA-27 alloy composites was investigated. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer under unlubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of samples were examined by the scanning electron microscopy (SEM). The test results revealed that those composite specimens exhibited significantly lower wear rate than the ZA-27 matrix alloy specimens in all combinations of applied loads and sliding speeds. The difference in the wear resistance of composite with respect to the matrix alloy, increased with the increase of the applied load/sliding speed and Al₂O₃ particle content. The highest degree of improvement of the ZA-27 alloy tribological behavior corresponded with change of the Al₂O₃ particles content from 3 to 5 wt%. At low sliding speed, moderate lower wear rate of the composites over that of the matrix alloy was noticed. This has been attributed to micro cracking tendency of the composites. Significantly reduced wear rate, experienced by the composite over that of the matrix alloy at the higher sliding speeds and loads, could be explained due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. Level of wear rate of tested ZA-27/Al₂O₃ samples pointed to the process of mild wear, which was primarily controlled by the formation and destruction of mechanical mixed layers (MMLs).     

Friction and Wear Properties of ZrO2�CAl2O3 Composite with Three Layered Structure Under Water Lubrication

Zirconia?CAlumina (ZrO₂?CAl₂O₃) composite with three layered structure was prepared, and its friction and wear properties under water lubrication were investigated. The results indicate that the layered composite exhibited better tribological properties comparing with ZrO₂?CAl₂O₃ mono-layered composite at same tested conditions. Good combination of toughness and strength as well as subsequently excellent friction and wear properties were mainly contributed to the residual stress of the layered composite, which caused by thermal mismatch of sintering between layers through special design of compositions and structure. Friction coefficient and wear rate of the layered composite decreased with increment of load and/or velocity. The change of tribological properties was also relative to wear mechanisms, micro-cutting, and abrasive wear were main mechanisms at lower load and/or lower velocity but fatigue wear caused by plastic deformation became dominant at higher load and/or higher velocity.     

Thermal oxidation of Zr-2.5Nb alloy and its biotribological properties

Zirconium alloys are potential materials for permanent implants due to their suitable mechanical strength, good biocompatibility, and superior corrosion resistance. However, Zr-2.5Nb alloys are greatly limited to the applications of artificial joints due to their poor tribological properties. Thermal oxidation is considered as a good way to improve the tribological properties of Zr-2.5Nb alloys. The effect of temperature on the properties of thermal oxidized Zr-2.5Nb alloys was investigated to understand the growth mechanism of ZrO₂ coating. In addition, the surface hardness of the thermal oxidized Zr-2.5Nb alloys was examined. Finally, the tribological properties of the thermal oxidized Zr-2.5Nb alloys were investigated to evaluate the potential application in artificial hip joints. The results showed that ZrO₂ coating was successfully synthesized on the surface of Zr-2.5Nb alloys, and the temperature has significantly effects on the thickness of the ZrO₂ coatings. It also found that thermal oxidation could significantly improve the surface hardness and wear resistance of Zr-2.5Nb alloys.