Effect of deep cryogenic treatment on the formation of nano-sized carbides and the wear behavior of D2 tool steel

The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.

Carbide precipitation and microstructure refinement of Cr-Co-Mo-Ni bearing steel during hot deformation

The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.

Preparation of CaB6 powder via calciothermic reduction of boron carbide

The method of calciothermic reduction of B4C was proposed for preparing CaB6.The phase transition and morphology evolution during the reaction were investigated in detail.The experimental results reveal that Ca first reacts with B4C to generate CaB2C2 and CaB6 at a low temperature and that the CaB2C2 subsequently reacts with Ca to produce CaB6 and CaC2 at a high temperature.After the products were leached to remove the byproduct CaC2,pure CaB6 was obtained.The grain size of the prepared CaB6 was 2–3μm,whereas its particle size was 4–13μm;it inherited the particle size of B4C.The residual C content of the product was decreased to 1.03 wt%after the first reaction at 1173 K for 4 h and the second reaction at 1623 K for 4 h.

Influences of Cerium and Carbide on Mechanical Properties of Steels

s: The influences of cerium and cerium carbide on the strength, plasticity, impact toughness and other mechanical properties of steels were investigated by means of metallography, scanning electron microscopy, impact test, tensile test and other experimental methods. The results show that cerium in solid solution of the steel matrix can inhibit the grain growth of austenite and enhance the temperature of grain coarsening by fifty degrees at least. An excess of cerium addition will segregate to grain boundaries, and considerably reduce the impact toughness of the steel. The cerium carbide can obviously improve the plasticity and toughness of steels, but does not noticeably affect the yield strength of steels.

Particle Size and Crystal Phase Effects in Fischer-Tropsch Catalysts

Fischer-Tropsch synthesis （FTS） is an increasingly important approach for producing liquid fuels and chemicals via syngas-that is, synthesis gas, a mixture of carbon monoxide and hydrogen-generated from coal, natural gas, or biomass. In FTS, dispersed transition metal nanoparticles are used to catalyze the reactions underlying the formation of carbon-carbon bonds. Catalytic activity and selectivity are strongly correlated with the electronic and geometric structure of the nanoparticles, which depend on the particle size, morphology, and crystallographic phase of the nanoparticles. In this article, we review recent works dealing with the aspects of bulk and surface sensitivity of the FTS reaction. Understanding the different catalytic behavior in more detail as a function of these parameters may guide the design of more active, selective, and stable FTS catalysts.

Rapid manufacturing of SiC molds with micro-sized holes using abrasive water jet

Silicon carbide (SiC) is highly wear resistant with good mechanical properties, including high temperature strength, excellent chemical resistance, and high thermal conductivity and thermal shock resistance. SiC molds, which can be produced with diverse microstructural features, are now widely used in glass molding owing to their excellent characteristics, and also have potential applicability in IT industries. SiC molds are traditionally fabricated by silicon micromachining or dicing. The fabrication cost of silicon micromachining is very high, however, because several expensive masks are needed. Furthermore, the fabrication time is very long. Meanwhile, it is difficult to make micro-patterned molds with arbitrary shapes using dicing saws. Abrasive water jet (AWJ) is widely applied to cut and drill very brittle, soft and fibrous materials. It offers high energy density, the absence of a heat affected zone(HAZ), high performance, and an environment friendly process. In spite of these advantages, micro-hole drilling via conventional AWJ processing suffers from notable shortcomings. We proposed a new abrasive supplying method of AWJ. The proposed method reduces frosting phenomena, and provides micro-machining of AWJ. The characteristics of a hole machined was investigated by the proposed AWJ process according to the ratio of water and abrasives. With the optimal experimental conditions, 3×3 array SiC molds with the diameter of 700 μm and depth of 900 μm were successfully manufactured.

Effect of Pyrophyllite Particle Size on Properties of AI_2O_3-SiC-C Bricks for Iron Ladles

The Al2O3 -SiC-C bricks for iron ladles were pre-pared asing bauxite, fused corundum,pyrophyllite, SiC powder and flake graphite as main starting materials, and phenolic resin as binder. The effect of pyroph,yllite particle size on permanent change in dimensions, cold crushing strength, oxidation resistance, and corrosion resistance of Al2O3 - SiC - C bricks was investigated. The results show that with the decrease of the pyrophyllite particle size, the permanent change in dimensions of Al2O3 - SiC - C bricks decreases, cold crushing strength increases, the oxidation resistance at 1400 ℃ increases, and the corrosion resistance at 1500℃ decreases.

Mechanism of size effects of a filler on the wear behavior of ultrahigh molecular weight polyethylene

Although the size effects of a filler are closely related to the complex multi-level structures of their polymer composites;unfortunately,such relationships remain poorly understood.In this study,we investigated the effects of various sizes(40-600 nm)of silicon carbide(SiC)fillers on the wear behavior of ultrahigh molecular weight polyethylene(UHMWPE)in the presence of the silane coupling agent KH-560.All of these SiC fillers improved the wear resistance of UHMWPE significantly,with a medium size(150 nm)being optimal.To examine the reasons for this behavior,we analyzed the multi-level structures of the samples in terms of their matrix structures(crystalline;amorphous;interphase),matrix-filler interactions(physical adsorption;chemical crosslinking;hybrid network)and the external effects of SiC fillers(bearing loads;transferring frictional heat).The high rigidity and thermal conductivity of SiC fillers and,more importantly,the intrinsic characteristics of the matrix structures(larger crystal grains;higher interphase;stronger amorphous entangled networks)were the key parameters affecting the enhancement in the wear-resistance of the UHMWPE.Herein,we also provide interpretations of the corresponding physical effects.Our results should improve our understanding of the structure-property relationships and,thus,should guide the formula design of UHMWPE composites.

Effect of TiC particle size on microstructure and mechanical properties of 1%TiC_p/W composites

The nano-TiCp/W and micro-TiCp/W composites containing 1% TiC(mass fraction) particles with average particle sizes of 50 nm and 1.5 μm were fabricated respectively by high energy ball milling and vacuum hot pressing(VHP) at 2 373 K,30 MPa,in a vacuum of 1×10-3 Pa. Microstructure and mechanical properties of the composites were examined at room temperature. The results show that both n-TiC and μ-TiC particles are homogeneously distributed in the as-sintered composites. The size of n-TiC particle is about 100 nm,and that of μ-TiC particle is about 1 μm. The additions of n-TiC and μ-TiC particles both result in higher mechanical properties compared with monolithic W. The improved mechanical properties may be mainly attributed to the grain size strengthening,dispersion strengthening and grain boundaries strengthening. The addition of n-TiC particles to tungsten is found to have beneficial effects on the mechanical properties than that of μ-TiC due to its small size.

硬质合金六面顶顶锤研究进展

顶锤是超高压装置的关键部件和主要耗材,硬质合金材质以其高抗压、高刚度及优良的导热、导电性能成为顶锤的最佳材质。压机和合成腔体持续大型化,对顶锤质量及其使用又提出了更高的要求。文章综述了硬质合金顶锤相关研究进展。首先,从顶锤的材质设计、生产制造、产品后处理、新型微观结构方面,对顶锤材质与生产进行探讨,以提高顶锤质量;其次,从顶锤的几何参数与调整、受力与失效分析、新型外观尺寸入手,阐述优化顶锤尺寸设计,以改善顶锤的应力分布状态;最后,从去应力时效、过盈量、小斜面摩擦力、冷却水、叶蜡石尺寸等使用技术方面进行总结,以提高顶锤的使用寿命。

TiO_(2)添加量对SiC多孔陶瓷物相组成及性能的影响

为制备同时具有高气孔率和高强度的硅结合SiC多孔陶瓷,以α-SiC粉、单质Si粉及TiO_(2)粉为主要原料,在氩气气氛下经1400℃保温3 h制备SiC多孔陶瓷,探究TiO_(2)添加量(加入质量分数分别为0、2%、4%、8%)对材料物相组成、显微形貌、孔径分布及主要物理性能的影响。结果表明:随TiO_(2)添加量的增加,单质Si的衍射峰逐渐消失,材料中检测到Ti_(3)O_(5)及TiSi_(2)物相,伴随着新相的生成,SiC颗粒间结合更加紧密,其显气孔率及平均孔径减小,力学性能显著提升。当TiO_(2)添加量为8%(w)时,材料具有优异的综合性能,其显气孔率、常温抗折强度及平均孔径分别为33.6%、29.6 MPa和0.27μm。

Mo添加对WC-Ni硬质合金微结构及性能的影响

采用X射线衍射(XRD)、扫描电子显微镜(SEM)和性能检测等方法研究了不同Mo添加量对WC-Ni-Mo硬质合金的WC粒度、硬度、摩擦磨损和耐腐蚀性能的影响。结果表明:在研究的成分范围内(w(Mo)=1.5%~2.0%),WC的平均晶粒尺寸基本不随Mo添加量的变化而变化;随Mo添加量的增加,WC-Ni-Mo硬质合金的硬度略微有所下降,而摩擦磨损性能得到提升。Mo质量分数为2%的WC-Ni-Mo硬质合金在酸性溶液中的耐腐蚀能力要高于Mo质量分数为1.5%的合金,并且具有更好的电化学稳定性。总体来看,WC-8.0%Ni-2.0%Mo合金的综合性能优于WC-8.5%Ni-1.5%Mo硬质合金。

碳化硅晶片减薄工艺对表面损伤的影响

随着碳化硅功率器件和芯片技术的快速发展,对碳化硅物理强度、散热性及尺寸要求越来越高,因而,对碳化硅晶片的减薄处理逐渐成为晶圆加工的重要课题。由于碳化硅材料断裂韧性较低,在减薄加工过程中易开裂,碳化硅晶片的高效率、高质量加工成为急需突破的瓶颈。本文基于碳化硅晶片的磨削减薄工艺技术,从加工过程及基础原理出发,通过研究磨削减薄工艺中四个主要参数(砂轮粒度、砂轮进给率、砂轮转速和工作台转速)对晶片表面的损伤,如崩边和磨痕的影响,提出前退火减薄工艺,以提高晶片加工质量,降低晶片表面损伤。本研究工作揭示了晶片减薄工艺技术调控表面质量的方法,并在实验加工过程中验证成功,相关研究结果对加工难度大的硬脆材料晶片减薄技术具有重要的指导意义。

电石渣用于CFBB炉内脱硫的同步分解硫酸盐化行为研究

电石渣的性质和循环流化床锅炉(CFBB)的燃烧条件对电石渣的炉内脱硫效率和钙利用率的影响很大。系统研究了电石渣粒径、反应温度、CO_(2)浓度对电石渣同步分解硫酸盐化的影响,并分析了其影响机制。结果表明:电石渣会首先发生碳酸盐化反应生成CaCO_(3),随后CaCO_(3)分解为CaO,CaO继续发生硫酸盐化反应;粒径变化对电石渣的脱硫性能无明显影响;高温条件下(850℃、950℃)电石渣脱硫性能显著提高,钙利用率可达80.83%,低温条件下(650℃、750℃)电石渣的碳酸盐化反应与硫酸盐化反应存在竞争,不利于硫酸盐化反应的进行;当CO_(2)体积分数为55%和70%时,生成的CaCO_(3)分解受阻进而影响硫酸盐化反应,而当CO_(2)体积分数低于35%时,虽电石渣在前期的反应受CO_(2)浓度影响,但最终CO_(2)体积分数为35%与15%时的脱硫性能无较大差异。

Grain size effect on wear resistance of WC-Co cemented carbides under different tribological conditions

The grain-size dependence of wear resistance of WC-Co cemented carbides(with mean WC grain sizes of 2.2μm,1.6μm,0.8μm and 0.4μm,respectively)was investigated under different tribological conditions.The results showed that the grain size had opposite effects on wear resistance of the cemented carbides in dry sliding wear and microabrasion tests.In the former condition,with decrease of WC grain size hence the increase of hardness,plastic deformation,fracture,fragmentation and oxidation were all mitigated,leading to a drastic decrease in the wear rate.In the latter condition,pull-out of WC grains after Co removal dominated the wear,so that the hardness of cemented carbide was not a core factor.As a result,the wear resistance of the cemented carbide generally showed a decreasing trend with decrease of the grain size,except for a slight increase in the ultrafine-grained cemented carbide.Single-pass scratching of the cemented carbides under various loads indicated the same failure mechanism as that in the sliding wear tests.Furthermore,the reasons for severe surface oxidation of the coarse-grained cemented carbides were disclosed.

高碳铬轴承钢球化退火碳化物尺寸评级标准的对比讨论

本文对比分析制造业现行以下各标准关于高碳铬轴承钢碳化物尺寸规定:GB/T 18254-2016高碳铬轴承钢第5级别图退火组织,SEP 1520-1998钢中碳化物图谱系列显微检验法(斯凯孚公司D33标准总则采用同一标准),ASTM A892-09(2020)高碳轴承钢显微组织的定义和等级的标准导引及其附录金相图谱,舍弗勒公司轴承钢100Cr6球化退火显微组织标准(图谱)S 261010。对于球化退火碳化物尺寸评级,可见我国标准比国外标准级数少,且碳化物尺寸级差不均匀;我国企业通常要求第2级合格,碳化物尺寸偏大,并且显示偏聚程度较大和存在个别大颗粒;没有对超细球化退火组织碳化物级别的界定。需要结合我国轴承企业发展现状并参照国际先进标准,适当修订相关标准。

Precipitation Strengthening by Nanometer-sized Carbides in Hot-rolled Ferritic Steels

The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix and the characteristics of precipitated nanometer-sized carbides have also been examined by scanning electron microscopy and transmission electron microscopy. The precipitation regularity of nanometer-sized carbides has been studied by thermodynamic method and the contributions of corresponding strengthening mechanisms to the total yield strength have been calculated. The tensile strength of hot-rolled Ti-Mo ferritie steel can achieve 780 MPa with an elongation of 20.0% after being isothermally treated at 600 ℃ for 60 rain, and the tensile strength of Ti steel is 605 MPa with an elongation of 22.7%, according to the results of tensile tests. The critical nucleation size of （Ti,Mo）C is smaller than that of TiC at a given isothermal temperature, but the nucleation rate of （Ti, Mo）C is larger than that of TiC. The grainrefinement strengthening and precipitation strengthening contribute the main amount of the total yield strength. The major increase in yield strength with the decrease of isothermal temperature results from the contribution of precipi tation strengthening. The contribution of precipitation strengthening to the yield strength of the steels has been esti mated. The ferrite phase can be strengthened by about 400 MPa through precipitation strengthening in Ti-Mo steel isothermally treated at 600 ℃ for 60 rain, which is about 200 MPa higher than that of Ti steel under the same conditions.

Effects of Primary Carbide Size and Type on the Sliding Wear and Rolling Contact Fatigue Properties of M50 Bearing Steel

The influences of primary carbide size and type on the sliding wear behavior and rolling contact fatigue (RCF) properties of M50 bearing steel were systematically investigated under oil lubrication condition. A major breakthrough was achieved in the influence of primary carbide on tribological behavior. The opposite effect brought by primary carbide size on the sliding wear resistance and RCF life of M50 bearing steel was determined. Wear resistance increased with an increase in the studied primary carbide size, whereas RCF life decreased significantly. Compared with the 0 R and R positions with a relatively small carbide size, the wear volume of the 1/2 R position with a large carbide size was the smallest. Compared with the 0 R and R positions, the L10 life of the 1/2 R position decreased by 82.7% and 84.8%, respectively. On the basis of the statistical correlation between primary carbide size and the two tribological properties, a critical maximum carbide size of 5-10 μm was proposed to achieve optimal tribological performance. This research suggests that the equivalent diameter of the primary carbide should be controlled to be smaller than 10 μm, but further decreasing primary carbide size to less than 5 μm is unnecessary. The influence of primary carbide type in M50 bearing steel on sliding wear resistance was also discussed. Results indicate that the MC-type carbides with higher elastic modulus and microhardness exhibit better wear resistance than the M2C-type carbides.

Influence of Mo on Growth and Coarsening of Nanometer-sized Carbides in Low-alloy Ferritic Steels Containing Ti

By optical microscopy, transmission electron microscopy and energy dispersive spectroscopy, the changes with aging time in size, composition and distribution of nanometer-sized （Ti, Mo）C precipitated in Ti-Mo low-alloy ferritc steel have been studied in comparison with that of nanometer-sized TiC precipitated in Ti low-alloy ferritc steel. It was found that the growth rate of （Ti,Mo）C in Ti-Mo steel was less than that of TiC in Ti steel. Nanometer- sized carbides formed at 650 ~C （or 550 ~C） for 55 h were at transitional stage from growth to coarsening. When aging time reaches 55 h, the coarsening rates of nanometer-sized carbides in Ti and Ti-Mo steel tend to be the same and in- variable. The influence of Mo on growth and coarsening of nanometer-sized carbides tends to decrease with increasing aging time, and Mo contents in nanometer-sized carbides with the same size at different aging time were different.

硬质合金钢的性能与化学成分及WC晶粒度关系探讨

硬质合金材料具有优良的物理力学性能和化学稳定性能,其特性可通过改变成分与粒度来满足更大范围的工具性能需求,可根据加工方式不同调整硬质合金钢材料的主要特性,通过对比分析了钴含量及碳化钨晶粒度的大小对硬质合金钢物理力学性能的影响,介绍了一种含稀土元素的硬质合金钢材料的抗腐蚀性能和应用范围。结果表明,在硬质合金粉末中加入一些稀土元素可提高材料的抗氧化性能,还可控制WC晶粒的不均匀长大,细化晶粒。