Study of Wear Stabilisation in Cryoprocessed Cobalt-Based High Speed Steel

Cryogenic treatment is employed for high speed tool steels in order to enhance their wear resistance. The improvement in wear resistance is associated with a decrease in retained austenite and or by formation of eta-carbide/nano-scale carbides. In the present work, a complex alloyed high speed tool steel (M35) specimens were hardened at 1,200?°C, triple tempered at 400?°C, cryosoaked at ?185?°C for 4?C48?h and soft tempered (100?°C). The microstructure of the samples were characterised for hardness, carbide density, impact energy, wear loss and residual stress. Influence of these measured parameters on wear behaviour was studied to understand underlying wear mechanism. The cryotreated specimens exhibited mild to stable wear transition at 16?h and then subsequent wear stabilisation for all higher cryosoaking intervals.     

Effect of Deep Cryogenic Treatment on Wear Resistance of AISI 52100 Bearing Steel

In this study, the effects of deep cryogenic treatment (DCT) on the wear resistance of AISI 52100 bearing steel were investigated. For this purpose, a number of bearing steel samples were held for different times (12, 24, 36, 48, 60 h) at deep cryogenic temperatures (?145 °C). The wear experiments were carried out in a ball–disk arrangement, by applying loads of 10 and 20 N and a sliding velocity of 0.15 m/s. After conducting the experimental studies, 36 h was found to be the optimal holding time. At this holding time, the wear rate and friction coefficient were decreased, while the hardness reached to maximum values. It was observed that DCT led to significant microstructural changes, which resulted in improved tribological properties.     

固溶温度对GH742y合金组织及性能的影响

 研究了不同固溶温度对GH742y合金组织及性能的影响。结果表明：经1 140~1 180 ℃固溶处理后，GH742y合金中一次γ′相全部溶入基体，晶粒度明显长大到3~4级；采用(1 040±10)℃×4 h，AC+1 140 ℃×8 h，AC+850 ℃×6 h，AC+(780±10)℃×(10~16)h的热处理后，获得了均匀细小的γ′相，而且合金的综合性能最佳。     

Optimization of Cryo-treatment Parameters for PTFE by Quantum-Chemical Approach and Its Evaluation Through Mechanical, Thermal and Structural Characterization

Cryogenic treatment of polytetrafluoroethylene (PTFE) which is a widely used polymer in automotive applications is carried out using liquid nitrogen in order to improve its wear resistance. Hence, in this paper investigations on the influence of cryo-treatment especially on mechanical, structural and thermal properties of PTFE are presented along with the optimization of cryo-treatment parameters. The selected material is treated at different temperatures (?80, ?140, ?185?°C) for stipulated time period (4, 8, 12, 16, 20, 24?h) in the cryostat and then tested at ambient temperature. PTFE is also studied simultaneously for thermal ageing. The properties of ??un-treated?? and ??cryo-treated?? PTFE are evaluated in a comparative manner by experiments including wear performance, Tensile test, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetery. The result of quantum-chemical calculations for vibrational frequencies is used to match with experimental data for optimization of cryo-temperature. Thus cryo-treatment parameter, where the material showed thermodynamically most stable structure is optimized through quantum chemical approach. The change in crystallinity, crystallite size, bond lengths and bond angles are found to be the most important parameter responsible for enhancement of wear performance. Maximum increase in % crystallinity and wear performance is found at 12?h and ?185?°C, hence it can be considered as an optimum condition for cryo-treatment of PTFE.     

TiAl合金的热暴露表面及其对室温拉伸性能的影响

对TiAl合金的标准拉伸试样分别进行700℃ 100 h和750℃ 100 h的热暴露处理,观察表明,机械抛光试样的表面具有规则的抛光痕迹,经700℃ 100 h热暴露后试样表面生成絮状氧化物,表面仍可见机械抛光痕迹,而经750℃ 100 h热暴露后,试样表面生成较厚的、均匀分布的氧化层,该氧化层的显微硬度显著高于基体的显微硬度。由于合金的层片组织存在取向性,因而在氧化层与基体之间存在富铝的过渡层,有利于阻止基体的进一步氧化。测试结果表明热暴露在一定程度上降低了原抛光试样表面的残余压应力水平。拉伸结果表明,热暴露后试样的室温拉伸塑性普遍明显下降。分析认为,热暴露后合金塑性的下降主要归因于试样表面残余压应力水平的降低而弱化了表面压应力对拉伸中表面裂纹萌生的抑制作用,750℃ 100 h热暴露试样承载能力的明显降低与拉伸中氧化层与基体的界面处出现的连续裂纹有关。     

Influence of Cryoprocessing on Mechanism of Carbide Development in Cobalt-Bearing High-Speed Steel (M35)

Cryogenic treatment has been used commonly to high-speed tool steels to enhance the wear resistance of the materials. In the current research study, specimens of complex alloyed high-speed tool steel (M35) were hardened at 1473 K (1200 °C), triple tempered at 673 K (400 °C) and then cryogenically treated at 88 K (?185 °C) for varying lengths of period starting from 16 to 48 hours of cryosoaking followed by soft tempering at 373 K (100 °C). These treated specimens were studied as a function of cryosoaking period for their electrical resistivity, residual compressive stress, and its correlation with carbide density was established. TEM analysis indicated carbide size 0.156 to 1 μm, which confirms that the cryogenic treatment enhances the precipitation of finer carbides. Lower residual stresses in the higher carbide density regimes identified in 2D contour map were explained by the stress relaxation in the matrix through precipitation of incoherent carbides.     

Selection of Heat Treatment Process and Wear Mechanism of High Wear Resistant Cast Hot-Forging Die Steel

 Dry sliding wear tests of a Cr-Mo-V cast hot-forging die steel was carried out within a load range of 50-300 N at 400 ℃ by a pin-on-disc high-temperature wear machine. The effect of heat treatment process on wear resistance was systematically studied in order to select heat treatment processes of the steel with high wear resistance. The morphology, structure and composition were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS); wear mechanism was also discussed. Tribo-oxide layer was found to form on worn surfaces to reduce wear under low loads, but appear inside the matrix to increase wear under high loads. The tribo-oxides were mainly consisted of Fe3O4 and Fe2O3, FeO only appeared under a high load. Oxidative mild wear, transition of mild-severe wear in oxidative wear and extrusive wear took turns to operate with increasing the load. The wear resistance strongly depended on the selection of heat treatment processes or microstructures. It was found that bainite presented a better wear resistance than martensite plus bainite duplex structure, martensite structure was of the poorest wear resistance. The wear resistance increased with increasing austenizing temperature in the range of 920 to 1120 ℃, then decreased at up to 1220 ℃. As for tempering temperature and microstructure, the wear resistance increased in following order: 700 ℃ (tempered sorbite), 200 ℃ (tempered martensite), 440 to 650 ℃ (tempered troostite). An appropriate combination of hardness, toughness, microstructural thermal stability was required for a good wear resistance in high-temperature wear. The optimized heat treatment process was suggested for the cast hot-forging steel to be austenized at 1020 to 1120 ℃, quenched in oil, then tempered at 440 to 650 ℃ for 2 h.     

Multiphase Microstructure Optimization to Enhance the Mechanical Properties of AISI M35 High-Speed Steel

It is crucial to conduct in-depth research on the cryogenic-treatment mechanism to promote the standardization and industrialization of cryogenic treatment in the high-speed steel (HSS) industry. In this study, the microstructure and mechanical properties (microhardness and impact toughness) of AISI M35 HSS after deep-cryogenic treatment (DCT) and conventional heat treatment (CHT) are investigated, and the microstructural characteristics at different stages of CHT and cryogenic treatment are studied. It is indicated in the results that DCT of the steel leads to the formation of fresh martensite from residual austenite, as well as the introduction of more dislocations due to plastic deformation. In addition, the deep-cryogenic-treated specimen that is tempered shows increased numbers of martensite blocks and secondary carbide precipitation. The carbides in the steel are mainly V-rich (MC), W–Mo-rich (M₆C), and Cr-rich (M₂₃C₆). The hardness of the deep-cryogenic-treated samples increases by approximately 50 HV₁ because of the transformation of residual austenite and dislocation strengthening. Furthermore, specimens that are both deep-cryogenic treated and tempered exhibit a 30% increase in impact toughness and a more uniform distribution in hardness, likely due to the more homogeneous precipitation of secondary carbides and refinement of martensite.     

ECAP制备TWIP钢的力学性能研究

采用ECAP方法对TWIP钢(30Mn-3Si-3A1)试样进行一道次等径角挤压(ECAP)变形,对比研究原始态、一道次挤压态、ECAPlP+850℃×1h(空冷)处理和ECAPlP+1000℃×1h空冷处理后的微观结构及力学性能.试验结果表明:在变形过程中,形变孪晶的相互形变阻力和位错在形变孪晶界的大量塞积,使TWI...     

Effect of Centrifugal Speed in Abrasive Wear Behavior of Al-Si5Cu3/SiC Functionally Graded Composite Fabricated by Centrifugal Casting

Centrifugal casting was adopted for fabricating AlSi5Cu3/10 wt% SiC functionally graded metal matrix composite under three different centrifugal speeds of 800, 1000 and 1200 rpm, and hollow cylindrical components (φ_out 150 × φ_in 132 × 150 mm) were obtained. Microstructures of outer and inner periphery of all composites were observed through optical microscope and micro hardness of outer, intermediate and inner region of composite was tested using Vicker’s hardness tester. Results revealed that outer region of the composites centrifuged at all speeds have particle rich region with higher hardness. Abrasive wear experiments were conducted only on surface of particle rich region based on Taguchi’s technique by varying parameters such as centrifugal speed of casting process, rotating speed and applied load of abrasive wear tester. Analysis of variance results revealed that, centrifugal speed had highest significance on wear rate. Abraded surfaces were examined using scanning electron microscope and the maximum wear resistance was observed on particle rich zone of composite centrifuged at 1200 rpm.     

Effects of Aluminization Via Thermo-Chemical Diffusion on the Wear Behavior of Structural Materials for High-Temperature Gas-Cooled Reactors

We explore the effects of thermo-chemical aluminization on wear resistance of candidate alloys Incoloy 800HT and Inconel 617 for high-temperature gas-cooled reactor (HTGR) components. Aluminized samples were conditioned for 22 days in a once-through helium loop to simulate oxidizing conditions of HTGRs. The tribological performance of unconditioned and conditioned samples was tested using pin-on-disk tribometer in an air environment at 750 °C for 800HT and 900 °C for 617. Aluminized 800HT exhibited superior wear resistance compared to that of the as-received 800HT due to harder Fe-Al intermetallic compounds that formed at the surface of the alloy. Aluminized 617 exhibited wear resistance superior to that of the as-received 617 at higher loads but inferior resistance at lower loads. Conditioned 800HT as well as aluminized and then conditioned 800HT exhibited negligible wear when the protective oxide remained intact during tribotesting. When the oxide wore through, aluminized and then conditioned 800HT exhibited superior wear resistance compared to that of conditioned 800HT due to the increased hardness of intermetallic zones. Aluminized and then conditioned 617 exhibited inferior wear resistance compared to that of conditioned 617 due to significant ceramic wear of the aluminum oxide. Connections between surface hardness, chemical composition, initial friction coefficients, and wear resistance are established.

     

温度对40Cr钢温挤压成形的摩擦--磨损性能影响

采用温挤压技术对40Cr钢进行成形试验，考察了不同温度下温挤压试样的摩擦-磨损行为.通过扫描电镜、能谱仪和X射线衍射仪分析了40Cr钢磨损后表面形貌、化学元素分布和物相组成，讨论了40Cr钢温挤压的磨损机理.结果表明，在挤压温度为550℃时试样晶粒尺寸细小，残余奥氏体含量较高，硬度最高，其磨损性能为最佳；而当温度为650℃和750℃时，晶粒尺寸较粗大，残余奥氏体含量降低.在5N载荷作用下，挤压温度为550℃时，摩擦因数为0.7667；当挤压温度达到650℃，摩擦因数为0.8587，提高了12.01%，磨损性能降低；750℃时，摩擦因数为0.8764，相比550℃提高了14.31%，磨损性能进一步变差；在550、650和750℃时，磨损形式主要为磨粒磨损.      

Effect of Deep Cryogenic Treatment on Wear and Corrosion Resistance of an Al–Zn–Mg–Cu Alloy

Russian Journal of Non-Ferrous Metals - The 7075 aluminum alloy was subjected to deep cryogenic treatment (DCT) at –196°C with liquid nitrogen for different hours. The wear and corrosion...     

氮化硅铁对无水炮泥性能影响的研究

根据无水炮泥的基本配合比,分别用不同比例的氮化硅铁替代其中的刚玉作基质料,在埋炭条件下经110℃×24 h,900℃×2 h处理,以及在通氮气条件下经1500℃×2 h煅烧后,分别检测和分析了试样的物理性能。结果显示,试样的烘干强度最大,中温强度最低,高温强度介于两者之间。随着氮化硅铁含量从4%递增到12%,试样经过1500℃高温处理后,其常温耐压强度和抗折强度均呈递增趋势,当氮化硅铁含量为10%时达到最大值,体积密度则呈下降趋势,同时试样的抗渣渗透性能和抗渣侵蚀性能得到了提高,试样的钻孔开口时间逐渐缩短。     

Microstructural Characterization and Properties Evaluation of Ni-Based Hardfaced Coating on AISI 304 Stainless Steel by High Velocity Oxyfuel Coating Technique

The present study concerns a detailed investigation of microstructural evolution of nickel based hardfaced coating on AISI 304 stainless steel by high velocity oxy-fuel (HVOF) deposition technique. The work has also been extended to study the effect of coating on microhardness, wear resistance and corrosion resistance of the surface. Deposition has been conducted on sand blasted AISI 304 stainless steel by HVOF spraying technique using nickel (Ni)-based alloy [Ni: 68.4 wt pct, chromium (Cr): 17 wt pct, boron (B): 3.9 wt pct, silicon (Si): 4.9 wt pct and iron (Fe): 5.8 wt pct] of particle size 45 to 60 ??m as precursor powder. Under the optimum process parameters, deposition leads to development of nano-borides (of chromium, Cr₂B and nickel, Ni₃B) dispersion in metastable and partly amorphous gamma nickel (??-Ni) matrix. The microhardness of the coating was significantly enhanced to 935 VHN as compared to 215 VHN of as-received substrate due to dispersion of nano-borides in grain refined and partly amorphous nickel matrix. Wear resistance property under fretting wear condition against WC indenter was improved in as-deposited layer (wear rate of 4.65 × 10^?7 mm³/mm) as compared to as-received substrate (wear rate of 20.81 × 10^?7 mm³/mm). The corrosion resistance property in a 3.56 wt pct NaCl solution was also improved.     

低温盐浴渗氮对Custom 465钢耐蚀及耐磨性的影响

为了提高Custom 465马氏体沉淀硬化不锈钢的耐磨性,分别在440、480和520℃对580℃时效后的样品进行了2 h的盐浴渗氮,使用显微硬度计、X射线衍射仪、电化学工作站、球盘式摩擦磨损仪、表面轮廓仪、扫描电镜等设备,研究渗氮温度对Custom 465钢表面物相、硬度、渗层显微形貌、耐蚀性及耐磨性的影响.随着渗氮温度升高,耐蚀性逐渐降低,但表面硬度增加,520℃处理后表面硬度增大到1240 HV,较未处理试样的400 HV明显上升,渗层厚度达到22μm.440℃渗氮后表面物相为氮在马氏体基体中过饱和的α'_N,点蚀电位降低约60 m V;480℃时有少量CrN相析出,引起点蚀电位降低约180 mV,同时磨损体积下降约43%;520℃时CrN相的含量明显升高,自腐蚀电位降低约70 mV,无明显的稳态钝化区,磨损体积降低82%,减磨效果明显.      

成型工艺对树脂基摩擦材料及其摩擦学性能的影响

以碳纤维2.5D浅交弯联结构为预制体,分别采用树脂传递成型工艺(RTM)和热压成型工艺(HPM)制备了碳纤维增强酚醛树脂基摩擦材料.通过MS-T3001摩擦磨损试验机考核了材料的摩擦磨损性能,采用扫描电子显微镜、激光三维形貌扫描仪观测了材料的磨损形貌,对比分析了两种成型工艺对材料摩擦学性能的影响.结果表明:随着滑动速度和工作载荷的增大,材料的摩擦系数均减小.热压成型工艺成型摩擦材料的主要磨损形式为磨粒磨损,摩擦系数0.085~0.130,磨损率1.5×10-8 g·N-1·m-1.树脂传递成型工艺成型摩擦材料的主要磨损形式为黏着磨损和疲劳磨损,摩擦系数0.075~0.120,磨损率7.5×10-8 g·N-1·m-1.      

氢电极预烧温度对丝网印刷YSZ电解质薄膜的影响

采用丝网印刷法制备了Y2O3稳定ZrO2(YSZ)电解质薄膜,并对固体氧化物电解池(SOEC)的NiO-YSZ氢电极预烧温度进行了优化。结果表明,NiO-YSZ氢电极适宜的预烧温度为1 000℃,YSZ电解质薄膜化后制备的SOEC在800℃、850℃和900℃三种电解温度下,1.50V时的产氢速率分别为386mL/(cm2.h)、255mL/(cm2.h)和142mL/(cm2.h)。采用丝网印刷法将YSZ电解质薄膜化制备后可以有效降低电解池的欧姆阻抗。     

Simultaneous identification of antibodies to Brucella abortus and Staphylococcus aureus in milk samples by flow cytometry

Two flow cytometric assays are described herein. The single cytometric test (SCT) detects antibodies to either Brucella abortus or Staphylococcus aureus in the serum or milk of a cow or water buffalo. The double cytometric test (DCT) detects both anti-B. abortus and anti-S. aureus antibodies concurrently. In the SCT, the sample to be tested is incubated in succession with the antigen (either B. abortus or S. aureus) and the proper secondary antiserum (fluorescein isothiocyanate-labelled rabbit anti-cow immunoglobulin antiserum or rabbit anti-water buffalo immunoglobulin antiserum). In the DCT, the sample to be tested is incubated first with B. abortus and S. aureus antigens and then with the secondary antiserum. The B. abortus antigen used in the DCT is covalently bound to 3-microm-diameter latex particles. The difference in size between B. abortus and S. aureus permits the establishment of whether the antibodies are directed against one, the other, or both antigens. When compared to the complement fixation test, the SCT and DCT each show a specificity and a sensitivity of 100%. The SCT has been used previously to detect anti-S. aureus antibodies. Here its use is extended to the detection of anti-B. abortus antibodies. The DCT is described here for the first time. The DCT appears to be useful for large-scale brucellosis eradication programs. It offers the possibility of using one test to identify animals that are serologically positive for both B. abortus and S. aureus.     

热处理温度对W6Mo5Cr4V8In高钒高速钢组织与性能的影响

采用不同温度对用于数控机床的W6Mo5Cr4V8In新型高钒高速钢进行热处理,并进行显微组织、冲击性能和耐磨损性能的测试与分析。结果表明,随热处理温度从1 050℃提高至1 150℃,高钒高速钢的晶粒先细化后粗化,冲击性能和耐磨损性能均先提高后下降。热处理温度升高至1 080~1 150℃时,M2C型碳化物发生分解。热处理温度优选为1 080℃。与1 150℃热处理相比,热处理温度为1 080℃时高钒高速钢的冲击吸收功增大46%、磨损体积减小48%。