Effect of Alloying Elements on Thermal Wear of Cast Hot-Forging Die Steels

The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wear of cast hot-forging die steels. The wear rates decrease with an increase in chromium content from 3% to 4% and molybdenum content from 2% to 3%, respectively. With further increase of chromium and molybdenum contents, chromium slightly reduces the wear resistance and molybdenum severely deteriorates the wear resistance with high wear rate. Lower vanadium/carbon ratio （1.5-2.5） leads to a lower wear resistance with higher wear rate. With an increase in vanadium/carbon ratio, the wear resistance of the cast steel substantially increases. When vanadium/carbon ratio is 3, the wear rate reaches the lowest value. The predominant mechanism of thermal wear of cast hot-forging die steels are oxidation wear and fatigue delamination. The Fe2O3 and Fe3O4 or lumps of brittle wear debris are formed on the wear surface.

Research on Thermal Wear of Cast Hot Forging Die Steel Modified by Rare Earths

Thermal wear of cast hot-forging die steel modified by rare earths（RE） was studied and compared with commercially used die steels. The function of RE and the mechanism of thermal wear of cast steel modified by RE were discussed. The results showed that with increasing content of RE, the wear rate of cast steel reduced at first and then increased. By adding 0.05% （mass fraction） RE, the cast hot-forging die steel with optimum thermal wear resistance was obtained, which was better than that of H13 and 3Cr2WSV. The large amount of coarse inclusions, （RE）2O2S, resulted from excessive RE, which obviously deteriorated thermal wear resistance. The mechanism of thermal wear of the modified cast die steel is oxidation wear and oxide fatigue delamination. The wear debris are lumps of Fe2O3 and Fe3O4.

New Method for Evaluating Thermal Wear of Rolls in Rolling Process

A new method was developed by a thermal wear machine to evaluate the thermal wear of roils in steel rolling process. The steel strip and rolls were simulated by upper and lower heating disks. The upper heating disk could he kept at a temperature of over 900 ℃ by induction heating. The pressure between the disks as high as 323.2 MPa could be achieved and the slipping rate could be 12. 7 %. The thermal wear of high speed steel （HSS） roll material, the wear rate of the HSS roll, and the SEM morphology of a worn HSS roll surface were investigated. This method was useful and could be employed to simulate friction and wear between strip and roll during the strip rolling process.

Improving Wear Resistance of the Ni-base Thermal Spray-Welding Coating Using Rare Earths

By adding rare earth alloy and cerium oxide, the effect of rare earths on tribological properties of nickel base alloy layer was studied to approach the possibility of applying rare earths to Ni base thermal spray welding coating. Wear test results showed that the wear rates of the nickel base coating without rare earths were quite high, and the load bearing capacity of coating was low, in contrast, the wear rates of the coating with rare earths were low and the coating had higher load bearing capacity. The results show that rare earths can refine the structure of nickel base alloy, improve the interface of the coating and substrate.

Effect of Hot Deformation on Formation and Growth of Thermal Fatigue Crackin Chromium Wear Resistant Cast Iron

The formation and growth of thermal fatigue crack in chromium wear resistant cast iron was investigated, and the effect of hot deformation on the crack was analyzed by means of optical microscope and scanning electron microscope and high frequency induction thermal fatigue tester. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, hot deformation can improve the eutectic carbiders morphology and distribution, inhibit the generation and propagation of thermal fatigue cracks. In the experiment, the propagation rate of thermal fatigue crack reduces with the quantity of hot deformation increasing, which was analyzed in the point view of the activation energy of crack propagation.

Microstructure and wear resistance of electro-thermal explosion sprayed stellite coating used for remanufacturing

Electro-thermal explosion directional spraying was used to prepare the stellite coating on substrate of the AISI 1045 steel. The morphologies of cross-section and worn scar, porosity, distribution of elements, micro- hardness and wear resistance of the coating were determined by means of SEM, EDAX, micro-hardness tester and sliding wear tester. Because of the compact construction, good bonding and high hardness, the coating is characterized by good wear resistance. The results show that the mainly failure mode of the stellite coating is micro- plowing.

THERMAL CRACK AND WEAR OF RAIL WHEEL AND DEVELOPMENT OF THERMAL CRACKING PROOF WHEELS

The thermal cracking and wear mechanism of rail wheel tread have been studied.The results showed that the thermal cracking of rail wheel tread is related to the chemical composition (mainly the carbon content)and the hardness of the wheels.When the composite braking shoes are used,the rate of wear of the wheel tread is related to the fracture toughness of the newly-formed“white layer”i.e.the martensite.The thermal cracking proof wheels(55SiMn) so far developed has achieved significant operating results in practical use.

Influence of CeO_2 on the Microstructure and Wear Resistance of M_(80)S_(20) Thermal Spray and Thermal Spray Welding Coatings

The influence of rare earth oxide CeO_2 on microstructure and wear resistance of M_(80)S_(20) thermal spray and thermal spray welding coatings is studied using optical microscope,scanning electron microscope,X-ray energy dispersion spectroscope,X-ray diffractometer and wear testing machine.The results show that the addi- tion of 8% CeO_2 can improve the microstructure,microhardness and wear resistance of coatings significantly.

Study on the Thermal Fatigue Behavior of Hot Deformed Wear Resistance Cast Iron and Effect of Carbide

The thermal fatigue behavior of wear resistance cast iron with different quantity of deformation has been investigated. The results show that eutectic carbide is the main location and passage for initiation and extension of thermal fatigue cracks, approving that the more serious, the carbide breaks. The higher thermal fatigue resistance of wear resistance cast iron will be and thermal fatigue fracture belongs mainly to brittleness.

On－Line Identification of Grinding Burn and Wheel Wear Based on Grinding Chips Thermal Flow

The theoretical basis of the grinding chips thermal flow being regarded as the characteristic signal of on line identification is summarized. And on line identification of grinding burn and wheel wear based on the grinding chips thermal flow is introduc

Effect of RE Modification and Heat Treatment on Formation and Growth of Thermal Fatigue Crack in Wear Resistant Cast Iron Containing Low Alloy

The formation and growth of thermal fatigue crack and the function of RE and heat treatment in wear resistance of cast iron containing low alloy were investigated,and it was analyzed in view of the activation energy for the crack′s propagation. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides,and the cracks are grown by themselves spreading and joining each other. RE can improve the eutectic carbide′s morphology,inhibit the generation and propagation of thermal fatigue cracks,therefore,promote the activation energy for the crack′s propagation,and especially,which is more noticeable in case of the RE modification in combination with heat treatment.

单密封带滑靴高速应用的制约因素分析

为研究制约单密封带滑靴高速应用的因素,计入密封带磨损轮廓,建立了滑靴副流固热耦合动力学模型,分析了转速及密封带宽度对底面油膜厚度、运行姿态、支承刚度和泄漏的影响。结果表明:高转速下,滑靴离心力矩增大时,倾角增大,底面最小间隙减小;动压效应增强时,吸油侧间隙增大,油膜刚度降低,偏磨风险增大。密封带增宽可提高滑靴底面的支承刚度,但密封带外内径比超过1.6会导致底面油膜增厚、泄漏增加。研究认为,泄漏和偏磨是制约单密封带滑靴高速应用的主要因素;在宽密封带基础上,考虑微结构以限制楔形动压效应,可能是提高滑靴允用转速范围的有效途径。

Microstructure and Sliding Wear Behaviour of Ni(Cr)-TiB_2 Coatings Deposited by HVOF Spraying of SHS Powders

This work reports research concerning the microstructure and sliding wear behaviour of cermet coatings deposited by high velocity oxy-fuel (HVOF) spraying. Two cermets were prepared with the following target compositions namely, Ni (Cr)-65 wt.% TiB2 and Ni (Cr)-40 wt.% TiB2. Coating microstructures were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), whilst microhardness and sliding wear tests were performed on the coatings to evaluate their performance. The HVOF sprayed deposits had layered, splat-like morphologies typical of thermally sprayed cermets. Coatings consisted primarily of TiB2 particles in a nickel-based binder phase. Other minor peaks in the XRD patterns belong to TiB, Ni2B, NiTiO3 and Ti2Oj. The coatings exhibit an amorphous halo in the diffraction pattern between 2 values of 40° and 50°. Sliding wear behaviour was examined using a conventional ball-on-disc apparatus. A sintered ceramic ball (A12O3) was employed as the counterface. The Ni (Cr)-65 wt.% TiB2 coating had a lower wear rate than Ni (Cr)-40 wt.% TiB2 coating. This may be related to the larger sizes of borides. Wear scar morphologies, on both coatings were examined by using SEM and EDAX detecting in order to establish the wear mechanism. Wear is proposed to proceed by subsurface cracking in these coatings.

Microstructure and properties of thermal-sprayed NiCrWRE coatings

The powders of NiCrW and NiCrWRE alloys were flame sprayed on a medium-carbon steel substrate by thermal spray welding. The micro- structure and tribological behavior of coatings were studied experimentally by means of scanning electron microscopy （SEM）, field emission gun scanning electron microscope （FEGSEM）, and wear tests. The addition of CeO2 modifies the coating morphology from a needle-like structure to a roughly cubic morphology; the refining and purifying effect of rare earth elements makes the microstmcture more compact and finer. Analysis of the worn surfaces reveals that the coatings with CeO2 addition show improved abrasive wear resistance over those without CeO2. By adding CeO2, the hardness of the coatings is significantly increased, and the wear resistance of the coatings is enhanced.

Wear analysis of a side dam in twin-roll strip casting

Reducing wear on a side dam can prolong the casting operation life of a twin-roll strip casting process,thus reducing production cost and improving casting stability.To lengthen the service life of the side dam,it is necessary to understand the wear performance of the side dam material.To investigate the wear behavior mechanism of the side dam,in this study,the UMT-2 friction and wear tester was used to determine the relationship between the wear rate of the side-dam material and various parameters.Based on the roughness of the contact area between the side dam and the end of the casting rolls as well as on the amount of deformation of the side dam,which was derived using a thermal-deformation simulation model,the reasons for the uneven wear of the side dam were obtained.

Tribological Behavior of Thermally Sprayed WC Coatings under Water Lubrication

Thermally sprayed coatings have been used in various fields of industry for enhancing surface characteristics of materials and extending their service life. The contact surface of some mechanical equipment such as the fine pulverization equipment which is used in the woody biomass production process is required to have wear resistance in the water environment. Thermally sprayed coatings would be a good candidate to improve surface wear resistance under water lubrication. The objective of this study was to evaluate the tribological performance of thermally sprayed coatings under water lubrication. Thermally sprayed coatings which were classified into WC, WB and Ni spraying of three categories were compared with water-lubricated sliding test at a sliding velocity of 0.02 m/s and mean pressure of p0 = 10 MPa with a ring-on-disk apparatus. Thermally sprayed coatings showed comparatively high friction coefficient and well wear resistance under water lubrication. WC contained coatings showed better wear resistance than WB and Ni coatings. Thermally sprayed coatings showed obviously different mechanical properties and tribological behaviors, and the effect of wettability and hardness on tribological characteristics was discussed under water lubrication. Friction coefficient increased as the surface contact angle of thermally sprayed coatings increased. The wear rate decreased as the surface hardness of thermally sprayed coatings increased. Wear resistance of thermally sprayed coatings was excellent under water lubrication. WC contained coatings showed lower wear rate than WB and Ni coatings. WC-14CoCr coating showed the lowest wear rate.

航空超高强度钢表面防护技术的研究进展

超高强度钢同时具有高强度和高韧性,是航空航天领域的重要承载构件,在飞机起落架、主梁、传动件、承力螺栓等领域有着广泛的应用。由于其使用时经常暴露在海洋大气环境下,腐蚀现象比较严重,通过对其进行表面保护,可以有效地改善其耐蚀、耐磨等性能,延长相关零件的使用寿命。针对目前常用的几种表面防护技术(热喷涂、真空镀、电镀、化学镀、表面组织转化、激光熔覆、离子注入等),综述了这些表面防护方法对不同超高强度钢耐磨、耐蚀、氢脆、疲劳等方面的影响,分析了这些防护方法的优缺点,并对其今后的发展方向进行了展望。

Thermal Sprayed CNT Reinforced Nanocomposite Coatings – A Review

This review is done essentially to study results in the field of synthesis and characterization of Carbon Nanotubes (CNT’s) reinforced nanocomposite coatings using thermal sprayed coatings. CNT reinforced nanocomposite coatings produced by thermal spray process are being developed for a wide variety of applications, e.g. aerospace, automotive and sports equipment industries. It is anticipated that, if properly deposited, nanocomposite ceramic coatings could also provide improved properties like wear resistance and thermal barrier coatings. These results clearly demonstrate that the significant improvement in coating performance can be achieved by utilizing proper thermal sprayed nanocomposite coatings. Thermal sprayed nanocomposite coatings shows improvement of resistance to wear, erosion, corrosion and mechanical properties. The purpose of this paper is to review CNT reinforced nanocomposite coatings using thermal spray by various researchers.

增材制造单晶镍基高温合金微观组织、热稳定性及耐磨性能

利用定向能量沉积的增材制造方法制备了单晶镍基高温合金SRR99,通过微观组织表征、硬度测量与纳米划痕实验,系统地研究激光增材制造单晶镍基高温合金在服役温度下的组织稳定性。结果表明:经过服役温度(650℃)退火100 h后,增材制造样品γ'强化相的形貌及尺寸(70 nm)依旧保持。相比于传统铸造样品,服役温度退火前后增材制造样品的硬度(6.6 GPa)均提高了20%以上。此外,退火前后增材制造样品的摩擦因数均具有数值低(0.19)、离散性小的特点。本研究证明定向能量沉积增材制造的单晶镍基高温合金样品拥有优异的组织热稳定性和耐磨性能,为激光增材制造技术应用于单晶镍基高温合金涡轮叶片的榫头修复与提性延寿提供了实验支撑。

基于耐磨性的聚晶金刚石刀具热损伤研究

为了研究PCD刀具钎焊热损伤程度对耐磨性的影响,设计单因素试验探究恒温时间、钎焊温度对热损伤的影响规律,定量分析热损伤程度对耐磨性的影响。结果表明:钎焊温度和恒温时间对PCD刀具的热损伤影响显著,其中钎焊温度对热损伤影响最大;PCD刀具钎焊过程中结合剂Co及其氧化物脱落形成的凹坑会降低刀具耐磨性,当产生穿晶裂纹和沿晶裂纹两种热损伤形式时,刀具耐磨性急剧降低;PCD刀具耐磨性较热损伤程度更为敏感,其变化率至少是热损伤变化率的1.2倍。