Eddy-current testing of the wear resistance of laser-hardened carburized chromonickel steel and the quality of laser hardening of drill bits

Features of eddy-current testing of carburized chromonickel steel 30XH3A subjected to processing with continuous laser radiation, subsequent treatment with cold at s-196°C (reducing the content of retained austenite in the carburized layer from 25–40 to 5–10 vol %), and tempering in the temperature range 100–400°C are studied. It is shown that the eddy-current method can be used to detect the presence of a laser-hardened wear-resistant layer on the steel surface and evaluate an abrupt decrease in the abrasive wear resistance of steel hardened with laser radiation, additionally treated with cold, and then exposed to low-temperature tempering. The possibility of eddy-current testing of the quality of laser hardening of roller paths of the bearing unit of rock-drilling bits manufactured from carburized steel 20XH3A using an attachable transducer with a protruding rod core is established.     

Microstructure and sliding wear behaviour of Tribaloy T-800 coatings deposited by laser cladding

This work has focused on the obtainment of Tribaloy T-800 coatings by laser cladding on plane 18/8 stainless steel specimens (AISI 304). The appropriate selection of cladding parameters allowed defect-free coatings to be obtained with minimal dilution. In order to evaluate their microstructure, cross-sections of the coatings were examined by optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The elemental composition of the coatings was determined using an optical emission spectrometer with an excitation source (GDOES) and phase analysis was performed by X-ray diffraction (XRD). Several zones can be distinguished in the microstructure of the clad layer: a planar crystallization region at the interface with the substrate, followed by cellular and dendrite crystallization from the interface to the surface of the laser track and an overlap zone between tracks which is characterised by the coarsening of the structure and the formation of a lamellar eutectic phase. The mechanical properties were evaluated by hardness measurements and sliding wear tests (ball-on-disk and block-on-ring configurations) at room temperature and without lubrication. It was observed the great hardness (close to 850 HV_0.3) achieved for the Tribaloy 800 laser coatings, which presented a wear coefficient (k) between one and two orders of magnitude lower than the substrate. The analysis of the clad worn surfaces showed that there was a transition from an adhesive-oxidational mechanism to a more severe plastic deformation and crack formation wear process with increasing the applied load.     

激光熔覆合金表面耐磨性试验研究

使用CO2激光器对45#钢表面进行Co基和Ni基合金熔覆处理。利用销盘式摩擦试验机对激光熔覆表面进行摩擦磨损试验,研究干摩擦和润滑条件下磨损机理。Ni合金熔覆层比Co基耐磨性要好。润滑条件下,两种合金的耐磨性比干摩擦都得到很大提高。     

Influence of layer thickness on hardness and scratch resistance of Si-DLC/CrN coatings

Abstract

Multifunctional coatings, widely used in tribological applications, have their properties strongly influenced by the interaction of the system coating/substrate. The use of multilayered coatings has been pointed out as a solution for the problem of high internal stresses that can be generated in coated systems, in particular in the case of soft substrates. In multilayered coatings, a decrease in the stress gradient between substrate and coating improves adhesion. Moreover, the thickness of the coating has shown a strong influence on the tribological behaviour of the coated system. This paper, through widely used and efficient techniques, seeks to assess the influence of the thickness of different layers (DLC and CrN) on the response of a multifunctional coating. Si rich DLC and CrN coatings with different thicknesses were deposited on a steel substrate (AISI 1020) by Plasma Enhanced Magnetron Sputtering (PECVD). Scanning electron microscopy (SEM) and Raman spectroscopy (RS) were used in order to characterize the chemical composition and microstructure of the coatings. Instrumented indentation and scratch test techniques were used to measure hardness, elastic modulus, and adhesion of each layer. Critical loads were determined by visual analysis, using SEM in conjunction with the curves obtained in the scratch tests. The evaluation of the effect of the thicknesses of the layers allowed an optimised design of the multifunctional coated systems with improved durability.     

激光熔覆原位自生Ti-Al-Si复合涂层的微观组织和高温抗氧化性能

为提高钛合金的高温抗氧化性能,采用激光熔覆原位自生技术,在TC4钛合金表面自行设计并制备了原子百分比为Ti∶Al∶Si=41∶41∶18和Ti∶Al∶Si=35∶35∶30的两种涂层。通过XRD、OM、SEM表征了涂层的微观组织和物相组成;借助管式电阻炉测试了涂层和基体试样在800℃×24h×5次循环氧化条件下的高温抗氧化性能;结合氧化增重和氧化动力学曲线分析了涂层的高温抗氧化机理。结果表明,涂层主要由Ti5Si3、Ti7Al5Si12、Ti3Al、TiAl和TiAl3等物相组成。涂层中没有出现一般激光熔覆所产生的外延生长柱状晶组织,全部为细小等轴晶。在800℃×24h×5次循环氧化条件下,TC4基材单位面积的氧化增重约为35.1mg·cm-2,涂层的约为2.8mg·cm-2和3.3mg·cm-2。两种涂层的高温抗氧化性能较钛合金基材分别提高了12.5倍和10.6倍。激光熔覆原位自生Ti-Al-Si复合涂层能明显改善TC4钛合金的高温抗氧化性能。涂层抗氧化性改善的机理,一方面是表面生成了连续致密的TiO2、Al2O3、SiO2氧化层,阻碍了氧扩散;另一方面是提高了氧化层的黏附性,使氧化层不易从涂层表面剥落,对涂层未氧化部分起到了很好的保护作用。     

The influence of hardness on the resistance to wear by paper

Abrasive wear data for a wide range of materials sliding against paper are compared to establish a general dependence on hardness of the abraded material. Three regions for the hardness dependence are identified. In all three regions, the wear rate depends on (hardness)^?n. In the region for which the hardness of the abrasive is larger than that of the abraded material, n ≈ 1; in the region where the hardnesses are similar, n ≈ 10; in the region where the abraded material is harder, n ≈ 5.     

低压反应离子镀制备Ge1-xCx薄膜的硬度研究

应用低压反应离子镀的薄膜制备方法在G e基底上沉积了G e1-xCx薄膜,随着沉积速度在0.1nm/s~0.9nm/s之间变化,G e1-xCx薄膜的硬度在2.12 GPa~11.066 GPa之间可变,当沉积速率为0.9nm/s时,G e1-xCx薄膜最大硬度为11.066 GPa。XRD测试结果表明,沉积的G e1-xCx薄膜均为无定形结构。对薄膜稳定性和牢固度的测试表明,制备的G e1-xCx薄膜在具有较高的硬度的同时,也有良好的性能。     

激光熔覆高铬铸铁组织和硬度的研究

针对高铬铸铁铸造组织粗大,强韧性差,容易开裂的问题,进行了高铬铸铁粉末激光熔覆实验,对熔覆层的显微组织和硬度等性能进行了检测与分析,研究了不同扫描速度对熔覆层显微组织和硬度的影响,分析了多道搭接区和多层堆积区熔覆层显微组织的演变规律,揭示了多层堆积横截面的硬度分布规律。研究结果表明:通过激光熔覆可以获得晶粒细化、组织致密、无裂纹与气孔等缺陷、硬度高(可达580 HV0.2)的高铬铸铁熔覆层。将该工艺应用到零件表面强化领域,将大大提高零件的性能和使用寿命。     

激光熔覆Fe/(Ti,W)C复合材料的研究

采用CO2激光加工成套设备在45#钢板表面熔覆Fe基涂层和Fe/(Ti,W)C金属陶瓷复合涂层。研究了加入(Ti,W)C对涂层相结构、组织、显微硬度及耐磨性的影响。结果表明,Fe基熔覆层主要组成相为马氏体相,显微组织主要由均匀细小的树枝晶组成;而Fe/(Ti,W)C复合涂层主要由马氏体和(Ti,W)C两种相组成,显微组织主要为花瓣状组织,加入(Ti,W)C颗粒对熔覆层组织有明显影响;熔覆层显微硬度由HV0.2 670提升至HV0.2 900;耐磨性能也有显著提升。     

Coarse cemented WC particle ceramic-metal composite coatings produced by laser cladding

Coarse cemented WC particle (600–900 μm) ceramic-metal composite coatings with a thickness of 1.2–1.5 mm were cladded on 20Ni4Mo steel surfaces using a laser of power 2 kW, diameter 5 mm and traverse speed 4–20 mm s⁻¹. The weight fraction of WC particles was 67 wt%. Compared with the behaviour of cemented WC particles of the same size and ratio in atomic hydrogen welded coating (AHWCs), the WC particles in laser-cladded ceramic-metal coating (LCCCs) show a uniform distribution in the molten zone. The microhardness of WC particles in LCCCs is 13.7–16.2 GPa, and their sizes are almost unchanged, which indicates that little heat damage occurs during laser cladding. The abrasive wear results showed that LCCCs have superior wear resistance to AHWCs. The wear mechanisms for LCCCs and AHWCs are analysed and compared.     

Preparation,microstructure and tribological behavior of laser cladding NiAl intermetallic compound coatings

Nickel aluminide (NiAl) intermetallic compound coatings were in situ synthesized from pre-placed mixed powders of Ni and Al by laser cladding. The phase composition and microstructure of the NiAl coatings were studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The effects of laser cladding parameters on the microstructure and friction and wear behavior of the NiAl coatings were investigated. It has been found that laser power density had a crucial influence on the microstructure and friction and wear behavior of NiAl coatings. Namely, the NiAl coatings synthesized under a lower power density have more dense and fine microstructure, and lower friction coefficient and wear rate. Besides, the friction and wear behavior of the laser cladding NiAl coatings is highly dependent on applied normal load and sliding speed; and the resulting coatings sliding against Si₃N₄ in a ball-on-disc contact mode is more suitable for tribological application at a moderate normal load of 3–7 N and sliding speed of 0.16–0.21 m/s.     

The relationship between the abrasive wear resistance,hardness and microstructure of ferritic materials

The relationship between the abrasive wear resistance and bulk hardness of ferritic materials in the pearlitic and martensitic conditions has been investigated. For pearlitic materials the abrasive wear resistance and bulk hardness are dependent on the pearlite content and for martensitic materials the abrasive wear resistance and bulk hardness are dependent on the square root of the carbon content. Thus for each structure there is a linear relationship between abrasive wear resistance and bulk hardness, but it is suggested that the material microstructure has a greater influence on wear resistance than the bulk hardness.     

Structure and wear resistance of electron-beam nitrous coatings

The paper deals with the study of the tribological properties of nitrogen-containing austenite coatings deposited by electron-beam facing during abrasive wear and the sliding friction of a VK6 hard alloy indentor. The abrasive wear resistance of the nitrous coatings deposited by the electron-beam facing of steel 60Kh24AG16 powder in quartz sand is lower than that of the steel 65G coatings after hardening; it increases with increasing mass share of the filler. At contents of nitrided ferrovanadium of 10?C30 wt % the abrasive wear rate increases by 30?C50%, respectively. It is found that under a certain load applied to the VK6 ball indentor the friction coefficient and the shear resistance of the surface layer diminish. It is shown that under heavy specific loads applied to the ball indentor the nitrous coating faced from steel 60Kh24AG16 powder and composite nitrous coatings have wear resistance exceeding that of steels 110G13 and Kh18N10 by more than two and seven times, respectively. Based on the results of structural studies an explanation of the observed behavior of the nitrous coatings is proposed.     

机械振动辅助激光熔覆Fe-Cr-Si-B-C涂层的显微组织及界面分布形态

采用机械振动辅助激光熔覆复合改性新工艺,在45钢表面制备了单道Fe-Cr-Si-B-C合金涂层。借助X射线衍射(XRD)、扫描电镜(SEM)和能量分散谱(EDS)分析了熔覆层的物相组成、微观结构和元素分布,通过HVS-1000型显微硬度计测试了熔覆层的显微硬度。结果表明,熔覆层主要由α-(Fe,Cr)固溶体、M7C3(M=Fe、Cr)碳化物、Fe2B硼化物和少量Fe0.9Si0.1组成。在机械振动辅助作用下,熔覆层结合界面组织由平面晶向带状和柱状晶转变,振幅为0.13~0.18mm时的晶粒细化效果最为明显;熔覆层中增强相形态随着频率的增加由短杆状向颗粒状、层状、条状转变,分布形态由杂乱分布向弥散分布和网状分布转变。相比未加机械振动的熔覆层,机械振动下的熔覆层中气孔、裂纹减少,显微硬度提高了约13.9%。这些结果显示熔覆层中显微组织形态及其分布主要受振幅和频率协同作用的影响。     

Determination of influence of laser welding modes and powder material composition on wear resistance of coatings

The results of metallographic studies and laboratory comparative adhesion strength tests of the coating with the base and abrasive wear by Brinell–Havorth method of weld powder coatings on nickel base with a width of weld layer of 20–80 mm and a height of 3–9 mm in one pass and samples of 40Kh steel have been presented. The adhesion strength of coating with hardness of 38–42 HRC was 400–480 MPa. It has been revealed that, at a hardness of the weld layer of 58–61 HRC, the wear resistance of coatings is higher than that of 40Kh steel in normalized and the improved state by 10 and 4.6 times respectively.     

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive.The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.     

Micro-scale abrasive wear testing of PVD coatings on curved substrates

A method is presented which enables a micro-scale abrasion test to be used to measure the wear performance of a coating over a small region, typically of millimetre dimensions, on a curved surface. The method is also applicable to studies of the wear resistance of any bulk material with a surface having complex curvature. The technique is illustrated by measurement of the intrinsic abrasion resistance of thin PVD coatings of TiZrN, ZrNbN and TiNbN on both flat and cylindrical tool steel and flat stainless steel substrates. The ability to measure the wear resistance of both a coating and its substrate, independently of each other and by a single test, is confirmed by experiment.     

激光熔覆Ni/TiB2复合涂层的组织与性能研究

在45钢表面利用激光熔覆技术制备了Ni／TiB2金属陶瓷复合涂层，利用光学显微镜、扫描电子显微镜、能谱仪、显微硬度计等，分析了涂层的显微组织特征、元素的分布以及涂层的机理等，并对试样硬度进行了测定。结果表明，在合理的工艺参数下，超细TiB2的加入，细化了激光熔覆涂层的晶粒，熔覆层显微组织主要由细小的等轴晶组成，TiB2陶瓷颗粒分布在枝晶间，而分解后的Ti均布于枝晶内，通过细晶强化、固溶强化及第二相强化等，大大提高了涂层的硬度。     

Sliding wear behavior of Fe-Al and Fe-Al/WC coatings prepared by high velocity arc spraying

A comparative study was carried out to investigate the microstructure and tribological behavior of Fe-Al and Fe-Al/WC iron aluminide based coatings against Si₃N₄ under dry sliding at room temperature using a pin-on-disc tribotester. The coatings were prepared by high velocity arc spraying (HVAS) and cored wires. The effect of normal load on friction coefficient and wear rate of the coatings was studied. The microstructure and the worn surfaces of the coatings were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscope (EDS). The results showed that, the main phases in both coatings were iron aluminide (Fe₃Al and FeAl) and α. WC/W₂C particles were embedded in the matrix of the composite coating. With adding WC hard particles, the Fe-Al/WC composite coating exhibited higher wear-resistance than Fe-Al coating. But the friction coefficient of both coatings showed little difference. As the load increased, the friction coefficient decreases slightly due to a rise of friction contact temperature and larger areas of oxide film formation on the worn surface, which act as a solid lubricant. Increasing load causes the maximum shear stress occurring at the deeper position below the surface, thereby aggravating the wear. The coating surface is subjected to alternately tensile stress and compression stress during sliding, and the predominant wear mechanism of the coatings appears to be delamination.     

不锈钢表面多道激光熔覆Ni基涂层的组织与性能

为提高不锈钢的硬度和耐蚀性能,利用6 kW横流CO2激光器在1Cr18Ni9Ti表面进行了单道和多道Ni25WC35合金粉末熔覆.X射线能量色散分析(EDAX)和X射线衍射(XRD)分析表明,熔覆层主要由(Fe,Ni)固溶体和WC原位自生成的W2C组成,同时含有CrNiFeC,Cu3.8 Ni化合物和FeW3C,Ni2...