Microstructure and abrasive wear behaviour of iron base hardfacing

Abstract

The influence of the composition and heat treatment of overlays on the abrasive wear resistance of iron base hardfacing alloy overlays is reported. Overlays were deposited using a shielded metal arc (SMA) welding process on structural steel using two commercial hardfacing electrodes, i.e.Fe – 6%Cr – 0.7%C (H₁) and Fe – 32%Cr – 4.5%C (H₂). Abrasive wear resistance of overlays in as welded and heat treated conditions was tested using a pin on disc system against a 300 grade waterproof SiC polishing paper at different normal loads (1 – 4 N) and constant sliding speed 2.0 m s^-1. Optical microscopy was used to study the microstructure of overlays in as welded and heat treated conditions. SEM studies of wear surfaces were carried out to analyse wear mechanisms. It was found that the wear resistance of the high Cr – C coating is better than the low Cr – C hardfacing under identical conditions. Significant variation in hardness was noticed across the interface, indicating the effect of dilution. Hardness of the coating adjacent to the interface was found to be comparatively lower than the coating further away from the interface. Post-weld heat treatment enhanced the abrasive wear resistance.     

Characterization of mechanical properties of FeCrBSiMnNbY metallic glass coatings

This article investigates mechanical characteristics of Fe-based metallic glass coatings. A series of the coatings were fabricated by conventional wire-arc spray process. The microstructure of the coating was characterized by means of X-ray diffraction, scanning election microscopy equipped with energy dispersive X-ray analysis, transmission electron microscopy, and differential scanning calorimeter. The coating is very dense smooth, adhering well and with no cracking. The microstructure of the coating consists of amorphous phase and α(Fe,Cr) nanocrystalline phase. The nanocrystalline grains with a size of 30 to 60 nm are homogenously dispersed in the amorphous phase matrix. The crystallization temperature of the amorphous phase is about 545 °C. The mechanical properties, such as porosity, adhesive strength, microhardness, elastic modulus, and abrasive wear resistance, were analyzed in detail. The experimental results indicate that the coating has high microhardness (15.74 GPa), high elastic modulus (216.97 GPa), and low porosity (1.7%). The average adhesive strength value of the coating is 53.6 MPa. The relationship between abrasive wear behavior and structure of the coating is discussed. The relatively wear resistance of metallic glass coating is about 7 and 2.3 times higher than that of AISI 1045 steel and 3Cr13 martensite stainless steel coating, respectively. The main failure mechanism of metallic glass coating is brittle failure and fracture. The Fe-based metallic glass coating has excellent wear resistance.     

非晶态Ni-P-ZrO2复合镀层的耐磨性能

采用纳米ZrO2作为复合粒子,通过电镀方法制备非晶态Ni-P-ZrO2复合镀层,研究纳米ZrO2粒子及热处理温度对复合镀层耐磨性能的影响。结果表明:纳米ZrO2粒子的存在不影响镀层基质金属的非晶态结构;镀态下Ni-P镀层的磨损受黏着磨损和犁削磨损机制共同作用,耐磨性能较差,纳米ZrO2粒子的加入,缓解了镀层的黏着磨损和犁削作用,使磨损量大幅降低;非晶态Ni-P-ZrO2复合镀层在350℃热处理温度下已转变为晶态结构,镀层具有最高的耐磨性能,其磨损方式为磨粒磨损和脆性剥离。     

Microstructure and wear resistance of electrodeposited RE-Ni-Mo-P-B4C-PTFE composite coating

Abstract

The structure, hardness and wear resistance of RE-Ni-Mo-P-B₄C-PTFE composite coating have been studied by means of X-ray diffraction, scanning electron microscopy, abrasion testing and microhardness testing. The results show that the structure of RE-Ni-Mo-P-B₄C-PTFE composite coating experiences a transformation from amorphous via a mixture to crystalline as the heat treatment temperature is increased. Crystalline particles in the coating become gradually finer with the addition of B₄C, B₄C plus polytetrafluoroethylene (PTFE) and B₄C plus PTFE plus rare earths (RE), in that order. The hardness and wear resistance of the RE-Ni-Mo-P-B₄C-PTFE composite increase with increasing temperature, reaching peak values at 400°C and 300°C, respectively. The wear resistance of the composite coating is greatly superior to that of other traditional coatings.     

冷热循环处理对钛基非晶合金摩擦学性能的影响EI北大核心CSCD

钛合金的耐磨性较差,在钛合金活动部件表面制备钛基非晶合金涂层是一种保持钛合金优势又提升其耐磨性的选择。采用X射线衍射仪、差示扫描量热仪、SEM、摩擦磨损试验机,对冷热循环处理前后钛基块体非晶合金的组织结构与摩擦行为进行比较研究。结果表明:经过冷热循环处理后的钛基块体非晶合金仍然保持着完全非晶态,弛豫焓提升11%。冷热循环处理后钛基非晶合金的平均纳米硬度从6.84 GPa降低到6.59 GPa,平均弹性模量从118.70 GPa降低到103.43 GPa,但硬度与弹性模量的比值增大。冷热循环处理后,钛基块体非晶合金在5 N和10 N的载荷下磨损率减小了约10%。与TC4合金相比,其在5 N和10 N载荷下的磨损率分别减小了20%和50%。TC4合金由于硬度较低,呈现较为严重的黏着磨损。冷热循环处理后,钛基非晶合金的磨损机制从铸态的磨粒磨损为主向磨粒磨损、黏着磨损和氧化磨损共同作用转变,且随着载荷的增大,黏着磨损减轻,磨粒磨损占据主导。因此,冷热循环处理是提升钛基块体非晶合金摩擦学性能的一种有效方法。     

Structure and properties of laser-cladded Ni-based amorphous composite coatings

A (N_i0.6Fe_0.4)₆₅B₁₈Si₁₀Nb₄C₃ amorphous composite coating has been fabricated on a mild steel substrate by a laser cladding process under different heat inputs. Observation of the structure and phase showed that the thickness of the coating decreased and the amorphous fraction increased when the laser cladding heat input was lower. The cooling rate increases when the heat input decreases, which favours the formation of amorphous phase. Microhardness and wear resistance test results indicated that a lower heat input led to higher microhardness and better wear resistance of the coating. An average microhardness of 1187.0 HV0.2 was obtained with a heat input of 69?J?mm^–1.     

Influence of deep cryogenic treatment of high speed steel substrate on TiAlN coating properties

Deep cryogenic treatment in combination with classic heat treatment shows a significant improvement in wear resistance of high speed steel tools. The aim of this research was to investigate how the microstructure of the substrate tool steel material, which was altered by deep cryogenic treatment and plasma nitriding, influences the properties of TiAlN coating. The microstructure, topography and composition of the TiAlN coating were investigated using field‐emission scanning electron microscope, atomic force microscopy, XRD, and glow discharge optical emission spectroscopy. The coating adhesion was measured using the scratch test. The sliding wear resistance and the force required to break the coating were determined with the ball‐on‐flat method. Resistance to microabrasion was measured by free ball abrasion test. The results show that deep cryogenic treatment combined with plasma nitriding influence the adhesion of the TiAlN coating to the high speed steel substrate. Wear resistance tests show better wear resistance of deep cryogenic treated samples in comparison with conventionally heat treated ones.     

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.     

Effects of conventional and active screen plasma nitriding on properties of electroless Ni–B coating

Abstract

In the present study, the properties of nitrided electroless Ni–B coatings prepared by conventional plasma nitriding and active screen plasma nitriding were investigated. For this purpose, electroless Ni–B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then, some of the prepared coatings were plasma nitrided by conventional method and the other ones by active screen method under the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, post-treatments change the amorphous as deposited coating structure to a crystalline one, which increases microhardness and wear resistance. Employing plasma nitriding treatment on the coatings results in higher microhardness and superior wear resistance than conventional heat treatment. The sputtering of iron atoms during plasma nitriding process can be the main reason for these results. In addition, active screen plasma nitriding demonstrates less surface roughness and superior wear resistance than conventional plasma nitriding.     

CoCuFeNiTi高熵合金涂层的制备和性能研究

采用激光熔覆技术在40 Cr钢基材表面制备CoCuFeNiTi高熵合金涂层,使用SEM、XRD和EDS等手段分析涂层的显微组织和相组成,研究了涂层的制备工艺、显微硬度、耐磨损和耐腐蚀性能。结果表明：在激光功率为700 W、扫描速度为6 mm/s条件下制备的CoCuFeNiTi高熵合金涂层表面质量较好,涂层与基体之间形成了良好的冶金结合;这种涂层由FCC相、少量的Cu₄Ti相和微纳级富Cu析出相构成,具有典型的树枝晶显微组织,Cu元素在枝晶间偏聚并形成微纳级富Cu析出相;涂层的显微硬度约为438.83HV,是基体的1.7倍;涂层的磨损质量损失约为基体的1/2,表明这种涂层具有更高的耐磨损性能。涂层的磨损,以黏着磨损为主伴有一定程度的磨粒磨损;这种涂层在pH=4的酸性溶液和3.5%NaCl溶液中的耐蚀性均优于基体。     

粗晶TM52钢结硬质合金的冲击磨料磨损性能研究

系统对比研究了粗晶粒TM52钢结硬质合金与分别采用真空烧结和低压烧结制备的细晶粒TM52钢结硬质合金在不同冲击功工况下的抗磨料磨损性能与行为,并在对磨损面形貌进行电镜观察分析的基础上探讨了粗晶粒TM52钢结硬质合金的磨损机理。研究发现,粗晶TM52合金的抗磨料磨损性能随着冲击功的逐步提高呈现先下降后增强的变化规律,这与其高锰钢基体在高冲击功条件下的高硬化速率及硬化效果更快、更充分有关。相对于细晶粒钢结硬质合金,粗晶粒TM52钢结硬质合金在抗冲击磨料磨损方面具有明显的性能优势,尤其在高冲击功(3~4J/cm~2)条件下,耐磨性能可提高40%~80%。在此工况下磨损机制主要为碾碎性磨料磨损、擦伤式磨料磨损和疲劳磨损,凿削式磨料磨损不明显。     

Sliding behaviour of nanophased AISI M2 tool steel obtained by mechanomaking and hot isostatic pressing

Abstract

The friction and wear behaviour of a nanophased AISI grade M2 tool steel was studied under dry sliding conditions and compared with that of a conventional AISI M2 steel. The nanocrystalline steel was produced by mechanosynthesis followed by cold and hot isostatic pressing. Slider-on-cylinder tests were performed against a ceramic coated countermaterial under loads of 10, 20, and 30 N and sliding speeds of 0.3 and 1.2 m s^-1 up to 10 km sliding distance. The nanocrystalline material underwent mild wear with low coefficient of friction under all testing conditions. The commercial M2 steel displayed distance dependent transitions from a regime of mild wear with low coefficient of friction, to a regime of severe wear with high coefficient of friction. The first tribological regime was due to the formation of a layer of iron oxides on the worn surfaces. In this regime, the wear resistance of both steels is mainly dominated by the mechanical properties of the carbides which have high load carrying capability. The second tribological regime, observed in the commercial steel, was due to the formation of cracks both on the mechanically mixed layer and at a depth beneath this layer, which also led to the detachment of carbides from the matrix. This abrasive ‘third body’ produced high wear damage of the commercial steel under high applied loads.     

Effect of magnesium addition on wear behaviour of Al–70 vol.-%Al2O3p composites

Abstract

Inthisstudy, drysliding and abrasive wear behaviour ofAl-70 vol.-%Al₂O₃particulate composite alloyed with Mg was examined. The composites were produced by a pressure infiltration casting technique. The composition of the matrix varied between 0 and 8 wt-%Mg, and the diameter of the Al₂O₃ particulates was 60 μm. Dry sliding wear tests were carried out on an unlubricated M2 quality high speed tool steel disc by a pin on disc type wear tester. Abrasive wear tests were run by rubbing the composites on abrasive Al₂O₃ grains. The results of the wear tests revealed that, both dry sliding and abrasive wear resistance ofthe composites increased with increasing Mg content in the matrix.     

电刷镀Ni-CNTs/PTFE纳米复合镀层的摩擦磨损与耐腐蚀性能

再制造工程中很多表面镀层要求具有优异的摩擦磨损与耐腐蚀性能,利用纳米电刷镀技术在45钢基材上制备NiCNTs、Ni-CNTs/PTFE、Ni-WC/PTFE-CNTs复合镀层。采用XRD和SEM观察电刷镀复合镀层表面相结构和微观形貌,采用球盘式摩擦磨损试验机测试其在干摩擦条件下的摩擦磨损性能,采用动电位极化曲线研究其在3.5%NaCl溶液中的电化学腐蚀行为。结果表明:Ni-WC/PTFE-CNTs复合镀层耐磨性能最优,其次为Ni-CNTs/PTFE、Ni-CNTs复合镀层,均强于纯镍镀层;当CNTs质量浓度分别为1.5g/L和1.0g/L时,Ni-CNTs复合镀层分别表现出最优的摩擦磨损性能和最佳的耐腐蚀性能,Ni-WC/PTFE-CNTs、Ni-CNTs/PTFE复合镀层次之。纯镍镀层和Ni-CNTs复合镀层的磨损机制是粘着磨损,Ni-CNTs/PTFE复合镀层的磨损机制主要是粘着磨损,其次为磨粒磨损,Ni-WC/PTFE-CNTs复合镀层的磨损机制主要是磨粒磨损和接触疲劳磨损。     

Ni-金刚石复合涂层的结构优化及基础磨削性能

采用电沉积技术在304不锈钢基体上制备了Ni-金刚石复合涂层。通过金刚石掺入量、加厚镀时间优化了金刚石复合涂层结构,利用球-盘式摩擦磨损试验仪研究了优化后的金刚石复合涂层对不同材料偶件(GCr15、SiC、304不锈钢)的磨削性能。结果表明:金刚石掺入量为1.5g/L时,金刚石上砂均匀且密集;加厚镀15min时,金刚石埋入率约为2/3,附着强度较好,适合磨削加工;GCr15、SiC、304不锈钢3种材料偶件的磨损体积依次减小,分别为:0.353 76mm~3、0.315 90 mm~3、0.194 01 mm~3,金刚石复合涂层对GCr15有较好的磨削性能;金刚石复合涂层磨削GCr15、SiC、304不锈钢均发生了磨粒磨损,此外,GCr15还发生了微弱的化学磨损,不锈钢发生了较明显的化学磨损和粘着磨损。     

Particle effects on friction and wear of aluminium matrix composites

Particle effects on friction and wear of 6061 aluminium (6061 Al) reinforced with silicon carbide (SiC) and alumina (Al₂O₃) particles were investigated by means of Vickers microhardness measurements and scratch tests. Unreinforced 6061 Al matrix alloy was also studied for comparison. To explore the effect of heat treatment, materials subjected to three different heat treatment conditions, i.e. under-aged, over-aged and T6, were used. Multiplescratch tests using a diamond and a steel indentor were also carried out to simulate real abrasive wear processes. Vickers microhardness measurements indicated that T6 heattreated composites had the highest hardness. Single-scratch tests showed that the variation of friction coefficient was similar to that of Vickers hardness and the peak-aged composites exhibited the best wear resistance. The wear rate of fine particle-reinforced composites was mainly affected by hardness. However, the wear rate of large particle-reinforced composites was influenced by both the hardness and fracture of the particles.     

Controlled synthesis of microarc oxidation coating on Ti6Al4V alloy and its antifriction properties

Abstract

Ceramic coatings were fabricated on a Ti6Al4V alloy surface by microarc oxidation (MAO) in Na₂ SiO₃ – (NaPO₃)₆ aqueous solutions with and without NaAlO₂ additive using an AC power supply. The effect of NaAlO₂ on microstructure, composition, and homogeneity of ceramic coatings were characterised using SEM, XRD, and EPMA. The antifriction property of the coatings with optimised microstructure sliding against SAE 52 100 steel ball was investigated on a pin-on-disc friction and wear tester. The results show that the addition of NaAlO₂ into Na₂ SiO₃ – (NaPO₃)₆ solution assists the formation of more dense, uniform, and thicker coatings and increases rutile TiO₂ content in the coatings. The optimised coating sliding against the steel has a friction coefficient as low as 0.2 – 0.3 at an applied load of 0.5 N and sliding cycle below 2500, which is much smaller than that of uncoated Ti6Al4V against the same counterpart. The transferring of material from the softer steel ball onto the coating surface is the main wear event, while the microarc oxidation coating is characterised by slight abrasive wear and adhesive wear.     

Development of new material and heat treatment for tools ensuring high performance in hot seamless tube rolling

Abstract

A new technology has been developed to improve the life of tools used for high temperature steel rolling in seamless tube manufacturing. It is a joint technology combining a new chemical composition and a special heat treatment. The new steel tool material has high Cr, C, and Ni contents compared with those of the conventional tools in order to increase the volume fraction of carbide which increases wear resistance. Through the new heat treatment, the macroscopic distribution pattern of eutectic carbide changes from meshlike to granular form increasing resistance against crack propagation. The validity of the results in the laboratory has been verified on the production line.     

Production and properties of steel–TiC composites for Wear applications

Abstract

Fe–(WTi)C composite granules containing up to 80 wt-% carbide have been produced by a selfpropagating high temperature synthesis reaction. These can be readily distributed in conventional steel melts. Additions up to 17 wt-% carbide have been made to a 0·4 wt-%C steel which was subsequently cast and hot rolled to plate. The microstructures of cast, rolled, and heat treated. samples display a homogeneous distribution of carbides which do not significantly affect the rolling performance of the steels. The carbides and grain refinement in heat treated samples result in a marked improvement in mechanical properties. The most significant improvement as a fraction of carbide additions is seen in abrasive wear performance.

MST/3196     

电流密度对Ni-W合金镀层摩擦磨损性能的影响

现有的Ni-W合金镀层摩擦磨损性能研究较少涉及镀层制备条件的影响。在不同电流密度下采用脉冲电沉积法在45钢表面制备了Ni-W合金镀层,测试了Ni-W合金镀层在干摩擦及油润滑摩擦条件下的摩擦磨损性能,并观察磨损形貌,分析其磨损机理。结果表明:在干摩擦状态下,随着电流密度增加,Ni-W合金镀层的磨损量逐渐降低,但摩擦系数逐渐升高,45钢的磨损主要是黏着磨损中的擦伤磨损,Ni-W合金镀层主要为磨粒磨损,个别存在少量疲劳磨损;在油润滑摩擦状态下,随着电流密度增加摩擦系数保持稳定,磨损量逐渐降低,Ni-W镀层与45钢的磨损形式均为磨粒磨损,45钢存在少量疲劳磨损。