Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

Effect of surface treatment to inserted ring on Al–Fe bonding layer of aluminium piston with reinforced cast iron ring

In order to improve the bonding strength between piston alloys and cast iron ring of aluminum piston with reinforced cast iron ring,the different methods of the surface treatments(shot blasting and sand blasting) to the cast iron ring are experimented.The optical micrograph shows that an intermetallic layer and a ligulate shaped structure are formed between piston alloys and cast iron base ring.After sand blasting treatment,the ring surface is non-metal shiny,matte-like and has no obvious pits.The intermetallic layer thickness formed between piston alloys and cast iron is thinner and more equally distributed after sand blasting to the ring.The content of the graphite distributed the interfacial zone after the shot blasting treatment is little.With the increase of time by sand blasting,the hardness starts to slightly descend.The bonding strength of the sample by sand blasting is obviously higher than that by shot blasting and increases from 9.32 MPa to 19.53 MPa.

Influence of Semi-Solid Isothermal Heat Treatment on Microstructure of Gray Cast Iron

Materials serve as an enabling technology contributing to solutions in problems of concern to society. In this research, the effect of semi-solid isothermal heat treatment on graphite morphologies and matrix structure for gray cast iron were studied. Microstructure observations and measurements of flaky graphite morphology are reported as a function of isothermal heating time range of 5 to 25 minutes after isothermal heating temperature at 1163℃. The effect heating time, on the semisolid microstructures during partial re-melting was investigated. Flack graphite morphology was changed significantly by isothermal heating of gray cast iron at 1163℃ for heating time above 15 min resulting fine graphite morphology in matrix structure. Hardness increases with increasing heating time due to the amount of cementite and fine pearlite matrix for air cooled gray cast iron. The optimum heating treatment condition was achieved at the temperature of 1163℃ for the range of 15 to 20 min.

Microstructure of coupled Al/gray cast iron obtained by molding and its effect on mass loss

This study aims to consolidate the surface of gray cast iron with aluminum deposition by developing a method that combines the preparation and surface treatment in a single operation. The effect of the wall thickness of the castings on the microstructure of the formed layers was studied, and two thicknesses, 8 mm and 25 mm, were studied. The formation of a continuous and homogeneous rich aluminum layer on the surface of the cast iron was observed. The formed layer is composed of two successive zones identified as two proeutectoid phases FeAl+FeAl/FeAl2 and single-phase FeAl, which significantly increases the surface hardness. Furthermore, this change in surface composition makes it possible to reduce the mass of the immersed samples in a 1 M hydrochloric acid solution during different exposure times(1 to 4 days). Consequently, a clear improvement in the corrosion resistance of the treated layers is highlighted.

Influence of varying forms of bionic units on repairing remaining quenching surface of gray cast iron

In order to repair and reuse remaining quenching surface(RQS)divided into severely worn surface(SWun-S)and mildly worn surface(MWun-S)of abandoned gray cast iron guide rail,inspired by the bionic theory,varying forms of bionic units such as spot(Sp-S),striation(St-S),and reticulation(Re-S)were fabricated on RQS of gray cast iron through laser processing technology.Firstly,the microstructure,phase composition,and microhardness of bionic units and RQS were analyzed by optical microscopy as well as X-ray diffraction instrument and scanning electron microscopy,respectively.Secondly,the oil lubrication wear experiment was performed on homemade line reciprocating wear machine.The results demonstrated that the bionic units had a significant effect on improving wear resistance of RQS of abandoned guide rail due to the microstructure and higher hardness.In addition,the weight loss ratios of MWun-S,Sp-S,St-S,and Re-S samples were decreased by 36.72%,36.78%,62.26%,and 80.39%,respectively,compared with that of SWun-S sample.The mechanism of wear resistance enhancement was also discussed.

Effect of scanning speed during PTA remelting treatment on the microstructure and wear resistance of nodular cast iron

The surface of nodular cast iron （NCI） with a ferrite substrate was rapidly remelted and solidified by plasma transferred arc （PTA） to induce a chilled structure with high hardness and favorable wear resistance. The effect of scanning speed on the microstructure, micro-hardness distribution, and wear properties of PTA-remelted specimens was systematically investigated. Microstructural characterization in-dicated that the PTA remelting treatment could dissolve most graphite nodules and that the crystallized primary austenite dendrites were transformed into cementite, martensite, an interdendritic network of ledeburite eutectic, and certain residual austenite during rapid solidifica-tion. The dimensions of the remelted zone and its dendrites increase with decreased scanning speed. The microhardness of the remelted zone varied in the range of 650 HV0.2 to 820 HV0.2, which is approximately 2.3-3.1 times higher than the hardness of the substrate. The wear re-sistance of NCI was also significantly improved after the PTA remelting treatment.

Microstructure of Ni /WC Surface Composite Layer on Gray Iron Substrate

The surface infiltrated composite （Ni/WC） layers on gray iron substrate were fabricated through a vacuum infiltration casting technique （VICT） using Ni-based composite powder with different WC particles content as raw materials.The microstructures of surface infiltrated composite layer,the interface structures between surface composite layer and the substrate,the changes of macro-hardness with the increasing of WC content and the micro-hardness distribution are investigated.The infiltrated composite layer includes a surface composite layer and a transition layer,and the thickness of the transition layer decreases with the increasing content of WC.The thickness of transition layer with 20%WC content in the surface infiltrated composite layer was 170 μm which was the thickest for all transition layers with different WC content.The surface composite layer was mainly composed of WC,W2C,FeB and NiB,along with Ni-Cr-Fe,Ni （Cr） solid solution,Ni （Si） solid solution and Ni （Fe） solid solution.The transition layer was composed of Ni （Cr） solid solution,Ni （Fe） solid solution,Ni （Si） solid solution,Fe （Ni） solid solution and eutectic.The surface macro-hardness and micro-hardness of the infiltrated layer had been evaluated.The macro-hardness of the surface composite layer decreases with the WC content increasing,and the average macro-hardness is HRC60.The distribution of micro-hardness presents gradient change.The average micro-hardness of the infiltrated layer is about HV1000.

RESIDUAL AUSTENITE AND STRAIN-INDUCED MARTENSITE IN LASER HARDENING LAYER ON GRAY IRON

The distribution of residual austenite in the laser hardening laver on the gray cast iron and the change in the amount of residual austenite during sliding wearing have been investigated by X-ray diffractometer.The thin foils of the hardening layer worn down have been observed by electron microscopy.It was revealed that two types of martensite are strain-induced by slid- ing wearing under load of 1.72 MPa on the hardening layer of residual austenite.The strain induced martensite is profitable to improve the sliding wearing resistance.

Analysis of Laser Surface Hardened Layers of Automobile Engine Cylinder Liner

Gray cast iron that is used for automobile engine cylinder liners was laser surface hardened using Nd ： YAG quasi-continuous and CO2 continuous wave laser, respectively. The macromorphology and microstructure of the laser surface hardened layers were investigated using an optical microscope. Geometric dimensions including depth and width and microhardness distribution of the hardened layers were also examined in order to evaluate the quality of the hardened layers.

Application of Electron Beam Surface Technologies in the Automotive Industry

Progress in the beam deflection technique opens up new possibilities for the application of electron beam (EB) surface and welding technologies in the automotive industry. This development is based on three-dimensional high-speed beam deflection and fully automatic online process control. So, in the EB surface treatment three-dimensional energy transfer fields can be realised which take into account the contour of a component, the conditions of heat conduction and the load conditions. High flexibility, precision and reproducibility are typical characteristics. High productivity is achieved by the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. EB surface treatment is becoming more and more attractive and important especially in the automotive industry, and also in comparison to laser technologies. This paper deals with different EB surface technologies, for example hardening, remelting, surface alloying, dispersing or cladding of different materials such as steel, cast iron and different alloys of Al, Mg and Ti. Examples of applications in the automotive industry, especially engine components, will be discussed.

激光表面处理对球墨铸铁冲蚀性能的影响

研究了激光表面熔化处理的球墨铸铁试样在石英浆料中的冲刷腐蚀特性 .结果表明 ,经过激光表面处理的球墨铸铁与原球墨铸铁相比具有很高的硬度和较好的耐冲蚀磨损性能 ,当冲刷角度为 0°、冲刷速度在 0 .5 8～ 4.47m/ s范围内时 ,激光处理试样的耐磨性是球墨铸铁试样的 3倍以上 ;冲刷角度对激光处理球墨铸铁的冲蚀磨损性能有很大的影响 ,激光试样的磨损质量损失随着冲刷角度的增大而增加 ,当冲刷角度为 45°时 ,激光试样与球墨铸铁试样的单位磨损质量损失已很接近 ;在 p H值处于 4～ 7的范围内 ,激光处理试样的耐腐蚀磨损性能为球墨铸铁的 2～

表面处理状态对高铬铸铁轧辊氧化膜生长形态的影响

利用热重分析、扫面电镜研究了不同表面处理状态对高铬铸铁800℃高温氧化膜生长形态和剥落行为的影响。结果表明,与抛光表面相比,粗糙表面显著加速了氧化膜的生长速度和开裂倾向,改变了氧化膜生长形态。讨论了不同表面处理状态氧化膜的裂纹萌生机制。

铸铁表面激光淬硬的机制和条件

探讨了铸铁表面激光强化的机制,研究了不同铸铁表面层经CO_2连续激光辐照后的组织和性能的变化规律,提出了各种铸铁表面激光强化方案的选择原则。

铸铁表面渗铝及其高温抗氧化能力的研究

在研究HT200和QT450－10的渗铝工艺及测试试样渗铝后的高温抗氧化能力的基础上，考察了渗层的组织结构，分析了高温抗氧化规律，并运用最小二采法得到了试样单位面积氧化增重的经验公式，为渗层失效的判断提供了依据。

铸铁热浸渗铝及其抗高温氧化性能研究

为了研究热浸温度、时间及硅含量对HT200热浸渗铝的影响,用称重法分析了未镀、浸镀和浸镀加扩散退火处理铸铁的高温抗氧化能力,用金相显微镜和XRD分析了渗层组织结构。结果表明:镀层厚度随温度升高和时间延长而增大,本试验中浸镀温度740～810℃,浸镀时间5～10min较佳。硅抑制渗层的生长,当镀液硅含量为2%,6%和9%时,镀层厚度分别为384,200μm和121μm。渗层结构由外镀层和中间扩散层(以Fe3Al为主)组成,经扩散退火后,渗层主要为Fe2Al5相。浸铝和浸铝且扩散退火处理后的铸铁抗氧化能力提高2～8倍,耐蚀性显著改善。

影响铸铁导热性的工艺因素

详细分析了铸造过程中的工艺因素，尤其是熔炼、凝固和冷却条件对铸铁导热性的重 要影响。

汽车发动机汽缸的激光表面处理

以汽车发动机汽缸为对象，探讨了灰铸铁表面激光强化的机制，研究了不同工艺参数条件下铸铁表面经ＣＯ２连续激光辐照后硬化层深度变化及金相组织和显微硬度的变化规律。结果表明，铸铁表面经激光处理后，表层组织明显细化且硬度值显著上升。

等离子束表面处理对硼铸铁组织与性能的影响

研究了等离子束表面硬化工艺参数对硼铸铁淬硬层及其组织与性能的影响。实验结果表明:硼铸铁经等离子束淬火处理后,其硬化层的组织为隐针马氏体+残余奥氏体+片状石墨+硼化物,其显微硬度是未处理的2～3倍,且硬度分布沿硬化层深度方向很不均匀。在扫描速度不变的条件下,随电流增大,硬化层深度和宽度增加,显微硬度增大;在电流不变的条件下,随扫描速度增大,硬化层深度和宽度减小,显微硬度减小。

内燃机活塞环材料及其表面处理

活塞环在发动机中起着密封、控油、导热、支撑的作用,活塞环材料应具备良好的耐磨性、耐热性、耐蚀性、强韧性、导热性、工艺制造性以及与气缸材料的磨合性。球墨铸铁和钢材已经成为活塞环的基本材料,采用表面处理方法如镀铬、氮化、喷钼、喷涂陶瓷层等工艺进行表面改性来提高活塞环的使用性能。需要不断地研究和开发新型活塞环材料和表面处理工艺来满足发动机的发展需要。

加筋复合白口铸铁界面的结合强度

研究了在白口铸铁工件中埋入一定数量的钢筋制成加筋式复合白口铸铁的界面结合强度及其影响因素．实验表明，钢筋表面除锈后再经过3种防锈处理都能提高加筋复合白口铸铁的界面结合强度，但效果相差不大．正交试验结果表明，在镶铸工艺因素中，液固体积比（白口铁铁水体积：埋入钢筋的体积）对界面结合强度影响最大，浇注温度和钢筋预热温度也有显著的影响．