Influence of melt treatments and polished CVD diamond coated insert on cutting force and surface integrity in turning of Al-7Si and Al-7Si-2.5Cu cast alloys

The microstructures, machinability and surface characteristics of Al-7Si and Al-7Si-2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al-7Si-2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better machinability and surface characteristics in the cast condition compared with the same alloy subjected to only grain refinement or modification. Performances of the turning inserts (uncoated and polished CVD diamond coated) were evaluated in machining Al-7Si and Al-7Si-2.5Cu cast alloys under dry environment using a lathe. The polished CVD diamond coated insert outperformed the uncoated cutting insert which suffered from sizeable edge buildup leading to higher cutting force and poor surface finish. The polished CVD diamond coated insert shows a very small steady wear without flaking of the diamond film during cutting. This paper attempts to investigate the influence of grain refinement, modification and combined action of both on the microstructural changes in the Al-7Si and Al-7Si-2.5Cu cast alloys and their machinability and surface finish when different turning inserts are used.     

Sliding temperature and wear behaviour of cast Al–Si base alloy

Abstract

The influence of sliding interface temperature on friction and wear behaviour of eutectic (LM13) and hypereutectic (LM28) Al–Si base alloy in as cast and heat treated condition has been investigated. LM13 and LM28 alloys having nominal composition Al–12Si–1Ni–0.8Cu–0.6Mg and Al–17Si–1Ni–0.8Cu–0.6Mg used in this study. Wear and friction tests were performed under dry sliding conditions using a pin on disc type of friction and wear monitor with the data acquisition system conforming to ASTM G99 standard. It was found that sliding interface temperature has a close relation with wear and friction response of these alloys. Initial rise in temperature reduces the wear rate and as soon as a critical temperature (CT) is crossed, wear rate abruptly increases. The friction coefficient of both alloys first decreases with rise in temperature then subsequently increases beyond a certain temperature. The influence of temperature on wear behaviour in particular was found to be a function of alloy composition and heat treatment. For as cast LM28 alloy, the critical temperature (140°C) was found to be lower than that in the heat treated condition (180°C). A temperature–wear mechanism is proposed for these alloys.     

Wear behaviour of aluminium matrix TiB2 composite prepared by in situ processing

Abstract

The wear behaviour and microstructure of aluminium and Al-12Si alloy (A413) matrix composites containing 1 and 5 vol.-%TiB₂ particles have been investigated. The composites were prepared by an in situ reactive slag technique. The wear surfaces and wear products were studied after reciprocating and rolling - sliding tests. Wear resistance increased with increasing particle content, and the Al-12Si composites were more wear resistant than those with Al matrixes. The wear mechanisms are briefly discussed.     

Influence of melt treatments on sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures and dry sliding wear behavior of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu cast alloys have microstructures consisting of uniformly distributed α-Al grains, eutectic Al– silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited better wear resistance in the cast condition compared with the same alloy subjected to only grain refinement or modification. The improved wear resistances of Al–7Si–2.5Cu cast alloys are related to the refinement of the aluminum grain size, uniform distribution of eutectic Al-silicon and fine CuAl₂ particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the sliding wear behavior.     

Dry sliding wear behaviour of Mg–10Gd–3Y–0.4Zr alloy

In present work, the wear behaviour of a Mg–10Gd–3Y–0.4Zr alloy during dry sliding has been investigated. The experiments were carried out using Ball-on-Flat type wear apparatus against an AISI 52100 type bearing steel ball counterface in a load range of 3–15 N, sliding speed range of 0.03–0.24 m/s, temperature range of 298–473 K and at a constant sliding distance of 400 m. Analyses of the wear tracks, worn surfaces and wear debris of the Mg–10Gd–3Y–0.4Zr alloy were carried out using scanning electron microscope. As a comparison, the wear properties of common AC8A aluminium alloy under the same condition also presented. The results indicated that the Mg–10Gd–3Y–0.4Zr alloy exhibited low wear rate compared with cast+T6 AC8A aluminium alloy under the same condition. The wear rate of as-cast Mg–10Gd–3Y–0.4Zr alloy was lower than that of cast+T6 Mg–10Gd–3Y–0.4Zr alloy. The Mg₂₄(Gd, Y)₅ eutectic compound of as-cast Mg–10Gd–3Y–0.4Zr alloy could resist the material flow during friction and wear, and affected its wear rate. At high sliding speed, the retained wear debris was the major constituent of producing the severely deformed layers along the sliding direction. The trapped wear debris acted as a protective layer and reduced the wear rate.     

Microstructural alterations through heat treatment and its influence on wear response of a silicon containing zinc based alloy under different test conditions

Abstract

Observations pertaining to the influence of microstructural alterations brought about through heat treatment on the sliding wear behaviour of a zinc based alloy comprising of silicon have been analysed in this study. The effects of sliding conditions such as pressure and speed on the wear response of the alloy in as cast and heat treated conditions have also been investigated. The as cast alloy revealed dendritic structure consisting of primary α, eutectoid α + η, and ? phase. Silicon was present in the alloy microstructure as discrete particles. Heat treatment caused breaking of the dendritic structure and more homogeneous distribution of various microconstituents without affecting the morphology and mode of distribution of the silicon particles. The heat treated alloy attained superior wear response as compared with the as cast one especially under more severe wear conditions. Wear rate versus pressure plots revealed two slopes wherein the slope was low at low pressures and increased considerably beyond a critical pressure. The critical pressure decreased with speed while it was more for the heat treated alloy. The wear behaviour of the specimens deteriorated with pressure and speed. High wear rates were supplemented with severe surface/subsurface damage and coarse debris formation and vice versa. Changing microstructural features of the regions at different depths below the wear surface were attributed to the changing degree of deformation they experienced during wear. The wear behaviour of the specimens has been explained in terms of specific characteristics of various phases such as lubricating and load carrying capability, thermal stability and cracking tendency. Typical characteristics of worn surfaces/subsurface regions and debris further supplemented the specific wear behaviour of the alloy in different test/material conditions.     

Effect of processing on microstructure and wear characteristics of an Al-4·5Cu-10Pb alloy

An Al-4·5Cu-10Pb alloy was processed by spray forming as well as impeller mixing followed by chill casting methods. The microstructure, mechanical properties and dry sliding wear characteristics of the alloy were evaluated. The spray formed alloy showed an equiaxed grain morphology with a uniform dispersion of lead particles in the matrix phase. In contrast a cellular-dendritic morphology of the primary phase was the characteristic feature of the alloy processed by impeller mixing and chill casting method. The spray formed alloy indicated its superior mechanical properties and low wear rate particularly at higher applied load and sliding velocity. The possible reason for this behaviour is discussed in the light of microstructure of the alloy and the nature of the worn out surfaces of the wear test specimens.     

Unlubricated sliding of a titanium aluminide alloy against M2 tool steel

Abstract

This study is an extension of continuing research on the wear behaviour of gamma-TiAl base alloys, which has demonstrated how a surface reaction layer, made of native oxides, can dramatically improve the dry sliding wear resistance of the Ti-48Al-2Cr-2Nb-1B at.- alloy. The results presented provide a further insight on the wear behaviour of the coated alloy under different loading conditions. Moreover, specific attention has been paid to the study of the tribological coupling and of the wear mechanisms affecting an M2 steel counterface disc. The steel counterface is abrasively worn by the oxide asperities present on the alloy surface. Wear debris remains trapped between the sliding surfaces and gets oxidised. Therefore, wear debris may contribute to further accelerate the wear rate before leaving the system or being compacted on the wear tracks to form protective glazes. Once the main wear mechanism was clearly identified, some tests were conducted on alloy specimens which had their surface oxide mechanically smoothed. This operation proved to be very successful indeed. In fact as a result, not only did the gamma-TiAl alloy have a zero wear rate, but also a significant reduction of the abrasive contribution to the wear rate of the steel counterface was detected. Both these improvements were observed even at the highest load employed in the investigation 500 N.     

Wear properties of high pressure torsion processed ultrafine grained Al–7%Si alloy

In this paper, Al–7 wt% Si alloy was processed via high pressure torsion (HPT) at an applied pressure 8 GPa for 10 revolutions at room temperature. The microstructure and hardness of the HPT samples were investigated and compared with those of the as-cast samples. The wear properties of as-cast and the HPT samples under dry sliding conditions using different sliding distances and loads were investigated by reciprocated sliding wear tests.The HPT process successfully resulted in nanostructure Al–7 wt% Si samples with a higher microhardness due to the finer Al matrix grains and Si particles sizes with more homogeneous distribution of the Si particles than those in the as-cast samples.The wear mass loss and coefficient of friction values were decreased after the HPT process. The wear mechanism was observed to be adhesive, delamination, plastic deformation bands and oxidization in the case of the as-cast alloy. Then, the wear mechanism was transformed into a combination of abrasive and adhesive wear after the HPT process. The oxidization cannot be considered as a mechanism that contributes to wear in the case of HPT samples, because O₂ was not detected in all conditions.     

铝硅合金、铁基粉末冶金、灰口铸铁耐磨性对比

选用压铸铝硅合金、铁基粉末冶金、灰口铸铁进行摩擦对比试验。结果表明,在给定的滑动摩擦条件下压铸铝硅合金的耐磨性最高,加工硬化能力最强;铁基粉末冶金仅次于压铸铝硅合金;灰口铸铁的耐磨必琢加工硬化能力最差。     

激光熔敷Ti5Si3/NiTi2复合材料涂层的组织与耐磨性

以Ti-Si-Ni合金粉末为原料，利用激光熔敷技术在BT9钛合金表面制备出了以金属间化合物Ti5Si3为增强相，以NiTi2为基体的Ti5Si3/NiTi2金属间化合物快速凝固耐磨复合材料涂层，Ti5Si3/NiTi2合材料涂层的硬度高，组织均匀，致密，与基材之间为完全冶金结合，在干滑动磨损试验条件下具有很好的耐磨性。     

Microstructure and Wear Characteristics of Al-4.5Cu-5Pb Alloy

Al-4.5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray fOrmed alloys. Wear testing employing a pin-on-disc type set-up, reveaIs considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation     

离心铸造Mg2Si 和Si 自生增强锌基复合材料的组织与性能

采用热模金属型工艺, 离心铸造Zn-27Al-9.8Mg-5.2Si 和Zn-27Al-6.3Mg-3.7Si 合金, 获得了内层聚集大量块状初生Mg₂Si 、少量初生Si, 中层不含初生Mg₂Si 和初生Si, 外层含有初生Mg- Si 和初生Si 的自生锌基复合材料。离心铸造Zn-27Al-3.2Mg-1.8Si 合金, 获得了不含初生Mg₂Si 和初生Si 的单层材料。考察了复合材料的组织形貌, 检测了复合材料的硬度和耐磨性, 分析了复合材料的断裂模式。结果表明: 复合材料的内层因聚集大量的初生Mg₂Si 和初生Si 具有较高的硬度和较优的耐磨性。复合材料的断裂方式为脆性断裂, 含共晶Mg₂Si 和共晶Si 的中层在断裂中比含块状初生Mg₂Si 和初生Si 的内层经历了更多的塑性变形。      

Effect of nickel aluminides on tribological behaviour of Zn-Al alloy

Abstract

Zinc-aluminium alloys are known to possess excellent bearing properties, particularly at high load and low speeds. The present work investigates the effect of nickel additions on the dry sliding wear and friction characteristics of a Zn-Al alloy at low load and high speed. Along with grain refinement, the presence of nickel improves the adhesive wear resistance as well as the friction characteristics of the Zn-Al alloy. The tribological behaviour of the alloy is explained on the basis of the nature of its microconstituents.     

Microstructural evolution in ultrasonically processed in situ AZ91 matrix composites and their mechanical and wear behavior

AZ91 alloy matrix composites reinforced with phases formed in situ from the addition of Si particles were fabricated by solidification under ultrasonic vibrations. Application of high-intensity ultrasonic field to the melt resulted in optimized size, morphology and distribution of in situ formed Mg₂Si particles. The amount of Mg₂Si particles increased, its size was refined and the distribution became uniform. Heterogeneous nucleation from the addition of silicon particles and enhanced nucleation from rapid cooling refined the grain size of the matrix in the composites. Hardness and ultimate compressive strength of the composites increased as compared to that of the cast AZ91 alloy. Composites exhibited improved sliding wear behavior of under varying normal loads. Identified dominant wear mechanism at lower sliding velocities is abrasion. Improvement in mechanical and sliding wear properties of the composites is attributed to the refinement of both matrix and reinforcement phases and improved dispersion of the reinforcement under ultrasonic vibrations.     

Wear behaviour of an Al–12% Si alloy reinforced with a low volume fraction of SiC particles

Aluminium–silicon alloys reinforced with low volume fractions of SiC particles were prepared by the compocasting process. The wear behaviour of the unreinforced Al–12Si alloy and metal-matrix composites (MMCs) was investigated by using a block-on-ring test at room temperature under dry conditions. The results showed that the addition of a low volume fraction of SiC particles (2–8 vol%) is a very effective way of increasing the wear resistance of the matrix alloy. Metallographic examinations revealed that the wear zone of the Al–12Si alloy consists of both hardened and deformation layers. The depth of the hardened layer depended on the applied load and was in the vicinity of 10–50 μm. The formation of the hardened layer was related to the alignment and redistribution of fragmented eutectic phase to the surface region during sliding wear. Furthermore, the delamination of debris from the hardened layer was responsible for a higher wear loss observed in the Al–12Si alloy. The thickness of the hardened layer formed on the MMC specimens was reduced considerably by the incorporation of fragmented SiC particles. This layer exhibited higher hardness and wear resistance than that developed in the unreinforced alloy.     

Investigation on the mechanical properties and frictional performance of Ni–Cu–Si alloy

The microstructure evolution, mechanical properties and dry sliding behaviour of Ni–30Cu–xSi alloy have been investigated systematically. As the volume fraction of microscale second-phase particles and nanoscale precipitates increases, the hardness, yield strength and ultimate tensile strength of alloy are improved significantly but elongation is reduced. Through confocal laser scanning microscope and atomic force microscope, it is suggested that the wear mode changes from the mixture of abrasive and adhesive wear to single abrasive wear. Owing to the existence of netlike microscale second-phase particles which are more likely to split the matrix, the Ni–30Cu–5.5Si alloy exhibits an abnormal higher wear rate even with the highest hardness. The netlike structure which deteriorates the friction performance should be avoided in wear-resistant materials.     

Wear resistance of Fe-28Al-3Cr intermetallic alloy under wet conditions

Wear behaviour of iron aluminides (Fe-28Al-3Cr at.%) alloy has been investigated under wet conditions using ball on plate sliding wear tester. Wear resistance was examined against tungsten carbide (WC) ball sliding over the iron aluminide plate at room temperature. Wear tests were carried out at 3 N and 5 N load conditions at different sliding frequency of mating ball. The micromechanisms responsible for wear were identified to be microcutting, micropitting, and microcracking of deformed subsurface zones under wet conditions.     

Dry sliding wear behaviour of a conventional and recycled high pressure die cast magnesium alloys

The dry sliding wear behaviour of a conventional and a recycled magnesium alloy produced by high pressure die casting was assessed by ball-on-disc tests under three different loads at a constant sliding velocity. The recycled alloy showed a lower friction coefficient and a lower wear rate when compared to the conventional alloy. A higher hardness and a relatively higher volume fraction of β-phase with a denser distribution near the surface were the reasons for the improved wear behaviour.     

Adhesive wear behaviour of cast aluminium–silicon alloys: Overview

This paper describes the various technological aspects related to adhesive wear of cast aluminium–silicon (Al–Si) alloys. Number of hypothesis and theories proposed in the last two decades in order to explain the different phenomenon related with wear and friction, and influence of test parameters (such as load, sliding speed, counter-surface) and work material properties (like mechanical and metallurgical) on tribological behaviour of aluminium–silicon alloys have been presented and discussed.