Influence of valence electron concentration over the friction behaviors of quasicrystal and B2‐type approximants in Al–Cu–Fe ternary system

Quasicrystals and their approximants are Hume–Rothery compounds having similar valence electron concentration. According to the valence electron concentration criterion for approximants, some B2 superstructures can be regarded as a special group of approximants. The present paper reports on an investigation of dry friction behavior of this group of phases. The results are compared with the data from quasicrystalline and related crystalline phases with similar composition. Specifically, we show that samples containing the B2 structure and its superstructures exhibit friction coefficients that decrease with increasing e/a and reach a minimum at 1.86, the value of the quasicrystal. Therefore, quasicrystals and B2‐based approximants belong to one group of phases whose surface properties are mainly determined by electronic structure characteristics rather than crystal structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance and surface alloying characteristics of Cu–Cr and Cu–Mo powder metal tool electrodes in electrical discharge machining

The main objective of this study is to investigate the effect of Cu–Cr and Cu–Mo powder metal (PM) tool electrodes on electrical discharge machining (EDM) performance outputs. The EDM performance measures used in the study are material removal rate (MRR), tool electrode wear rate (EWR), average workpiece surface roughness (R_a), machined workpiece surface hardness, abrasive wear resistance, corrosion resistance, and workpiece alloyed layer depth and composition. The EDM performance of Cu–Cr and Cu–Mo PM electrodes produced at three different mixing ratios (15, 25, and 35 wt% Cr or Mo), compacting pressures (P_c = 600, 700, and 800 MPa), and sintering temperatures (T_s = 800, 850, and 900 °C) are compared with those machined with electrolytic Cu and Cu PM electrodes when machining SAE 1040 steel workpiece. Analyses revealed that tool materials were deposited as a layer over the work surface yielding high surface hardness, strong abrasion, and corrosion resistance. Moreover, the mixing ratio, P_c, and T_s affect the MRR, EWR, and R_a values.     

Development and postoperation state of Ni–Co–Cr–Al–Y plasma heat-resistant coating

The paper presents the results of studying the structure and physical and mechanical properties of a Ni–Co–Cr–Al–Y heat-resistant intermetallic compound coating, formed by the method of the high-energy plasma powder spraying on the working surfaces of turbine blades of a gas turbine engine in the initial state and after completing the designed resource (within ~28000 h), as part of a GTE-45-3 power unit of a thermal power plant (ОАО Yakutenergo).     

Experimental and theoretical analysis of friction stir welding of Al–Cu joints

This paper presents a study of friction stir welding of aluminium and copper using experimental work and theoretical modelling. The 5083-H116 aluminium alloy and pure copper were successfully friction-stir-welded by offsetting the pin to the aluminium side and controlling the FSW parameters. A theoretical analysis is presented along with key findings. The process temperatures are predicted analytically using the inverse heat transfer method and correlated with experimental measurements. The temperature distribution in the immediate surroundings of the weld zone is investigated together with the microstructures and mechanical properties of the joint. This was supported by a finite element analysis using COMSOL Multiphysics. In this study, two rotational speeds were used and a range of offsets was applied to the pin. The microstructure analysis of the joints was undertaken. This revealed some particles of Cu inclusion in the nugget zone. The energy dispersive spectroscopy showed a higher diffusion rate of aluminium towards the interface while copper maintained a straight base line.     

Thermo-mechanical treatments of Sc- and Mg-modified Al–Cu alloy welds

High-strength heat-treatable aluminum alloy AA2219 finds application in aerospace industries. Though it has good weldability, with alternating current–tungsten inert gas welding, the joint efficiency obtained is only 40%, particularly in thicker plates. In the present study, an attempt has been made to improve the weld metal properties by modifying the chemistry of fusion zone and post-weld thermo-mechanical treatments. Fillers were made through casting route by melting conventional 2319 filler with Sc and Mg. Two levels of Sc (0.3% and 0.6%) and four levels of Mg (0.3% to 0.6%) were varied. Compressive deformation was done on the fusion zone of the weld to get three levels of percentage of reduction (4%, 8%, and 12%). As welded specimens and welds after compressive deformation, those were subjected to post-weld aging treatments at 190ºC for different periods up to 100 h. Compressive deformation on the welds made with modified filler of 2319 with Sc and Mg resulted in significant improvement in the weld metal strength.     

Relations of counterface materials with stability of tribo-oxide layer and wear behavior of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

Dry sliding wear tests of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy (TC11 alloy) sliding against AISI 52100 and AISI M2 steels were performed under the load of 50–250 N at 25–600 °C. For two kinds of counterface materials, the titanium alloy presented totally different wear behaviours as the function of temperature. The appreciable variations of the titanium alloy sliding against different counterface materials were attributed the fact that a hard counterface caused unstable existence of tribo-layers by its microcutting action, thus resulting in the increase of wear rate. It is suggested that the hard counterface must be avoided as the counterface for the titanium alloy/steel sliding system.     

The influence of nitrogen concentration on microstructure and ultra-low friction behaviour of Fe–N thin films

The influence of nitrogen concentration on the microstructure, chemical and electronic properties of Fe–N thin films and their tribological behaviour are studied. Increasing the nitrogen concentration from 5% to 12%, results in the decrease in friction coefficient from 0.14 to 0.04, while wear life increases significantly. However, increase in nitrogen concentration to 32% results in the increase in friction coefficient to 0.1 and decrease in wear life. Therefore, lowest friction and longest wear life is observed in the film with 12% nitrogen, which is due to the formation of ε-Fe₂N phase having high bond strength and chemically passive surface.     

Microstructural evolvement and formation of selective laser melting W–Ni–Cu composite powder

W–Ni–Cu alloy (90 wt% W, 7.5 wt% Ni, and 2.5 wt% Cu) parts were successfully fabricated via selective laser melting method. Phases, microstructure, compositions, and laser forming parameters of laser melted samples were investigated. It was found that the W–Ni–Cu powder system was based on the mechanism of liquid solidification. This process was realized through full melting of W, Ni, and Cu particles under high laser energy input. However, using relatively lower energy input, particle bonding was realized through liquid phase sintering with complete melting of Ni–Cu acting as binder and nonmelting of W acting as structure. Due to the Ni–Cu solid solution phase that appeared in a wide range from 1,084 to 1,455 °C, a coherent matrix interface can be observed after solidification. The microhardness of laser-fabricated specimens varied with different powder layer thicknesses, resulting from the laser-treated condition and ability of trapped air in the loose powder bed to escape. The metallurgical mechanisms were also addressed.     

Effect of Tribo-Oxidation on Friction and Wear Behaviour of HVOF Sprayed WC–10Co–4Cr Coating

Tribology Letters - In current investigation, tribological properties of TiAl matrix composite reinforced with 15 vol%Ti2AlN and TiAl alloy prepared through in situ reactive method of...     

Effect of deformation martensite on the electrical and magnetic properties of plastically deformed chromium–nickel steel

Connection between the structural and phase changes in specimens of chromium–nickel austenitic steel and their magnetic and electrical properties has been studied. It has been established that electric resistivity can be used as an additional testing parameter for the phase composition of plastically deformed articles made of austenitic-ferritic steel. It has been shown that the emergence of an additional phase of strain-induced martensite leads to a significant increase in electric resistivity.     

An experimental study of process variables in turning operations of Ti–6Al–4V and Cr–Co spherical prostheses

Ti–6Al–4V and Cr–Co alloys are extensively used in manufacturing prostheses due to their biocompatibility, high strength-to-weight ratio and high resistance to corrosion and wear. However, machining operations involving Ti–6Al–4V and Cr–Co alloys face a series of difficulties related to their low machinability which complicate the process of controlling the quality levels required in these parts. The main objective of this paper is to study the influence of cutting parameters, machine tool control accuracy and metrology procedures on surface roughness parameters and form errors in contouring operations of Ti–6Al–4V and Cr–Co workpieces. The machining performance of the two biocompatible materials is compared, focusing the study on part quality at low feed per revolution and the stochastic nature of plastic deformations at this regime. The results showed a better surface roughness control for Ti–6Al–4V, whereas for Cr–Co alloys, the performance presents high variability. In the case of form errors (sphericity), contouring errors and metrology procedures are important factors to be considered for quality assurance. In addition, the study analyses the correlation of the machining performance with different sensor signals acquired from a low cost non-intrusive multi-sensor, showing a high correlation of signals from acoustic emission sensors and accelerometers in the machining of spherical features on Ti–6Al–4V parts. The findings of this research work can be taken into account when designing prostheses components and planning their manufacturing processes.     

Generation of electron beams with adjustable durations of 1.0–0.2 ns and current amplitudes more than 400 A

The conditions for forming subnanosecond electron beams with adjustable pulse durations in the vacuum-diode mode using a SLEP-150 generator were investigated. It was confirmed that the residual air pressure in the diode (～0.1 Torr or less) does not affect the amplitude and duration of the beam current when using a nanosecond voltage pulse. It was shown that increasing the air pressure in the diode from 0.1 to 6.0 Torr leads to a decrease in the full width at half-maximum (FWHM) duration of the electron-beam current from ～1.00 to 0.18 ns and a shorter delay of the beam generation moment relative to the voltage-pulse rise time. It was established that the amplitude of the first peak of the beam current behind the foil remained constant under these conditions. Its value was ≥400 A. It is shown that when the interelectrode gaps are optimal for vacuum diodes, the pulse duration at elevated pressures shortens due to the gap breakdown for a time of ≤200 ps.     

The Microstructure and Wear Characteristics of Cu–Fe Matrix Friction Material with Addition of SiC

The Cu–Fe matrix continuous braking friction materials using SiC as abrasive were fabricated by powder metallurgy technique, and the effect of content and size of SiC were investigated. The tribological properties of friction materials sliding against AISI 1045 steel ring were carried out on a block-on-ring tester at different loads and sliding speeds. The strengthening effect of nano-SiC (55 nm) was superior to that of micro-SiC (70 μm) of the tribological properties for friction materials. The friction coefficients of friction materials increased with increasing nano-SiC content. However, the wear rates decreased with increasing nano-SiC content and then increased when the content of nano-SiC particle exceeded 10 wt%. The specimen contained 10% nano-SiC had the best tribological properties at different testing conditions.     

Metallurgical and mechanical characteristics of cryogenically treated tungsten carbide (WC–Co)

This paper aims to present the metallurgical and mechanical characterization of cryogenically treated tungsten carbide (WC–Co) in terms of α-, β-, γ-, and η-phase particles and wear behavior, respectively. The specimens of commercially available uncoated WC–Co in the form of round turning inserts were procured and subjected to cryogenic treatment at two levels ?110°C (shallow treatment) and ?196°C (deep treatment) of temperature. The microstructures obtained after cryogenic treatments have been characterized with a prominence to comprehend the influence of cryogenic treatment on the nature, size, and distribution of α-, β-, γ-, and η-phase particles as compared to untreated specimen. The mechanical properties such as hardness and wear rate of the specimens have also been compared by performing Rockwell A hardness test and pin-on-disk wear test, respectively. Microstructures, hardness, wear rate, and analysis of worn surface divulge the underlying metallurgical mechanism responsible in improving mechanical properties of the WC–Co.     

Influence of the Addition of Vanadium Nitride on the Structure and Specifications of a Diamond–(Fe–Cu–Ni–Sn) Composite System

This article discusses the influence of the addition of vanadium nitride on the mechanical and operational properties of diamond composite material based on metallic bond comprised of iron, copper, nickel, and tin obtained by sintering in a mold at 800°C for 1 h with subsequent hot repressing. It has been established that the addition of vanadium nitride in the amount of 2 wt % to diamond–(51Fe–32Cu–9Ni–8Sn) increases the ultimate compressive strength from 846 to 1640 MPa and bending strength from 680 to 1120 MPa, as well as decreases the wear intensity of the composite material from 0.0069 to 0.0033 g/km. The mechanism of improving the tribological properties has been revealed.     

Corrosion and corrosion wear behaviour of plasma carburised Stellite 21 Co–Cr alloy

Abstract

Low temperature plasma surface alloying with carbon (i.e. plasma carburising) of Stellite 21 Co–Cr alloy was conducted at temperatures from 400 to 500°C for 15 h in a gas mixture of 98 vol.-%H₂ and 2 vol.-%CH₄. The surface treated layers were characterised by XRD, SEM and microhardness tests. The corrosion and corrosive wear behaviour of the plasma carburised Stellite 21 Co–Cr alloy were studied respectively using electrochemical tests and well designed reciprocating wear tests in 3·5% NaCl solution. The results show that low temperature (≤460°C) plasma carburising can improve the corrosion resistance of Stellite 21 alloy; the corrosive wear resistance of Stellite 21 can be enhanced by up to three times; and the best corrosive wear resistance is achieved at the highest treating temperature (500°C). The detailed studies on the wear tracks indicate that the corrosive wear process was dependent on the individual wear and corrosion, as well as the synergetic effect.     

Effects of cold working and heat treatment on microstructure and wear behaviour of Cu–Be alloy C17200

The effects of cold work process between aging and solution heat treatment on the microstructure, hardness and the tribologic behaviour of a copper–beryllium (Cu–Be) alloy C17200 were investigated. The wear behaviour of the alloys was studied using ‘pin on disc’ method under dry conditions. The results show that the formation of fine grained structure and γ phase particles enhances the mechanical properties of the alloy; nonetheless, they do not reduce the wear rate. This is attributed to the capability of the softer specimens to maintain oxygen rich compounds during the dry sliding test.     

Microstructures and High-Temperature Friction–Wear Performance of Laser-Remelted WC-12Co Coatings by HVOF

A WC-12Co coating prepared by high-velocity oxygen fuel (HVOF) was remelted with a CO₂ laser, and the surface–interface morphologies, plane energy spectrum, and phases of the coating were analyzed by means of field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The friction and wear behaviors of the WC-12Co coating were investigated at high temperature with a wear test, and the morphologies and the changes in chemical elements on the wear scar after the wear test were analyzed with SEM and EDS, respectively. In addition, the influence of high temperature on the coefficient of friction (COF) and wear performance is discussed. The results show that the substrate is closely bonded with the substrate after laser remelting (LR), which includes mechanical bonding accompanied by metallurgical bonding. The average coefficient of friction (COF) at 600, 700, and 800°C is 0.6832, 0.3957, and 0.1922, respectively. The wear mechanisms of WC-12Co coating at 600 and 700°C are adhesive wear, abrasive wear, and oxidative wear, respectively, and the wear mechanism of the coating at 800°C is serious oxidative wear.     

Wear characteristics of Cr3C2–NiCr and WC–Co coatings deposited by LPG fueled HVOF

Wear behavior of the HVOF deposited Cr₃C₂–NiCr and WC–Co coatings on Fe-base steels were evaluated by the pin-on-disc mechanism. The constant normal load applied to the pin was 49 N and sliding distance was 4500 m with velocity of 1 m/s, at ambient temperature and humidity. The specific wear rate of WC–Co coating was 3 mm³/N m and Cr₃C₂–NiCr coating was 5.3 mm³/N m. SEM/EDAX and XRD techniques were used to analyze the worn out surface and wear debris. The Fe₂O₃ was identified as the major phase in the wear debris. The wear mechanism is mild adhesive wear in nature.