A STEEL MATRIX WEAR RESISTANT COMPOSITE REINFORCED BY IN-SITU GRANULAR EUTECTICS

A new steel matrix wear resistant composite reinforced by in situ granular eutectics can be obtained by modifying with a Si-Ce-Ti compound in the steel melt. The result indicates that the in situ granular eutectic is a pseudo-eutectic of austenite and (Fe,Mn)3C, which is formed between austenite dendrites during solidification due to the segregation of C and Mn impelled by modifying elements. The quantity of in situ granular eutectic reaches up to 8%-12% and its grain size is in the range from 10um to 20um. The austenite steel matrix wear resistant composite reinforced by in situ granular eutectic (abbreviated AGE composite) and austenite-bainite steel mains wear resistant composite reinforced by in situ granular eutectic (abbreviated ABGE composite) are obtained in the as-cast state and by air hardening, respectively. The wear resistance of the AGE and ABGE composites can be more greatly increased than that of their matrix steels under low and medium impact working condition.

Corrosion Behaviour of TiC-Reinforced Hadfield Manganese Austenitic Steel Matrix In-Situ Composites

The corrosion behaviour of Hadfield manganese austenitic steel matrix composite reinforced with the varying amount of TiC and unreinforced Hadfield manganese austenitic steel matrix alloy has been evaluated in 3.5% NaCl aqueous solution with the pH value of 6 by the potentiodynamic polarization curves and linear polarization resistance measurements at a scan rate of 1 mV/s at room temperature (25°C ± 2°C). The corrosion rate of the composites is higher than that of their unreinforced matrix alloy and it increases with the increasing volume fraction of TiC. The poor corrosion resistance of the composites can be attributed to the galvanic effects between the matrix and reinforcement.

Influence of Adding Ti Powder in Preform on Microstructure and Mechanical Properties of Al_2O_3p/Steel Composites by Squeeze Casting

To improve the mechanical properties of alumina particulates reinforced steel matrix composite, Ti powder was added into the alumina preform, a 5140 steel matrix composite was fabricated by squeeze casting, and the influences of Ti powder on the microstructure, hardness and bending strength of the composite were investigated, compared with the composite without adding Ti powder. Applied Ti powder and alumina particulates were 10-25 μm and 100-180 μm in size, respectively. Both composites were successfully fabricated, however Ti powder addition increased the infiltration thickness of the composite. In the Ti contained composite, a TiC film in micron scale is formed on the surface of alumina particles, many TiC aggregates are dispersed in the steel matrix without obvious remaining Ti powder. The hardness and the three-point bending strength of the composite reach 49.5 HRC and 1 018 MPa, respectively, which are 17.9% and 52.4% higher than those of the composite in the absence of Ti addition. Fracture morphology shows that the debonding of alumina particulates is eliminated for the composite in the presence of Ti addition. Sessile drop test shows the average wetting angle between 5140 steel and that of Ti coated Al2O3 is about 82.15°, much lower than the wetting angle 150° between steel and pure Al2O3. Therefore, the increase in the mechanical properties of the composite is attributed to the improvement of Al2O3 p/steel interface wetting and bonding by adding Ti powder in the preform.

Mechanical Behaviour Modelling of an Mg-Stabilized Zirconia Reinforced TRIP-Matrix-Composite under Cold Working Conditions

In the present work, a new method to predict the stress-strain curves for three-phase materials has been developed. It was applied using the example of an Mg-stabilized zirconia reinforced TRIP-matrix-composite. The content of the ceramic phase was varied between 5% and 20%, whereas the particle size of the ceramic was selected to be 30 to 50 μm. The method is a further development of mixture rule for multiphase materials with more than two microstructure components. The prediction results were compared with the original method of mixture rule and with the IsoE-method. It is shown that the new method significantly improves the convergence compared to the standard method for mixture rule, even though it does not reach the accuracy of IsoE-method. Furthermore, there is an improvement of predicted convergence for large values of the total stress. Finally, a working map was designed for a quick graphical definition of the objective functions.

常见结构材料低温性能研究进展

随着深空探测、极地科考、低温贮运等低温领域的快速发展,对低温材料的要求越来越高,低温材料逐渐成为目前国内外的研究热点。本文综述低温钢、铝合金、钛合金、铝基复合材料以及树脂基复合材料等常见结构材料的低温性能,归纳不同晶体结构、合金种类、合金元素等因素对结构材料的低温强度、塑性与韧性等力学性能的影响及低温变形和强韧化机理,介绍不同种类低温结构材料在国内外重要领域的应用,提出了低温材料未来的研究展望。

基体对ZTA_(p)/钢基复合材料磨损性能的影响

研究不同基体成分对空间结构复合材料冲击磨料磨损性能的影响。采用挤压铸造法制备复合区内基体Cr含量不同的空间结构ZTA_(p)/40Cr钢基复合材料,经850℃淬火及200℃低温回火,进行冲击磨料磨损试验,并和纯高锰钢进行比较。结果表明:复合区中基体Cr含量由2wt%、5wt%、15wt%逐渐升高时,复合材料的体积磨损率分别为8.02×10-4、5.37×10-4、5.46×10-4 cm3/min,趋势为先降低,然后趋于稳定。而高锰钢体积磨损率则为7.57×10-4 cm3/min,因此,含5wt%Cr复合材料耐磨性比高锰钢提高了41%。分析表明:具有一定Cr含量的ZTA_(p)/40Cr钢基复合材料磨损机制主要为磨料磨损,强韧适中的基体能保证良好的支撑和吸能,与增强相互相协同,使得复合材料的耐磨性提高。

高温处理对聚乙烯纤维-钢纤维高韧性水泥基复合材料抗折性能的影响

为了探究高韧性水泥基复合材料经高温处理后的力学性能,采用聚乙烯纤维与钢纤维混杂方式制备一种混杂纤维高韧性水泥基复合材料,通过三点抗折试验探讨所制得聚乙烯纤维-钢纤维高韧性水泥基复合材料经温度20、60、100、150、200、250℃处理后的抗折性能。结果表明:随着处理温度的升高,该复合材料的开裂应力、峰值应力和弯曲韧性均表现为先增大后减小的变化规律,处理温度为60、150℃时最大开裂应力为12.09 MPa,最大峰值应力为18.52 MPa;峰值应力受处理温度的影响较显著,当处理温度为200、250℃时,聚乙烯纤维熔化,复合材料的峰值应力相较于处理温度为150℃时的分别减小42.7%、57.9%;该复合材料的弯曲韧性在指定挠度为L/150、L/100(其中L为支座间跨度)阶段受处理温度影响较小,在指定挠度为L/50、L/25阶段,随着处理温度的升高而先增大后减小,聚乙烯纤维熔化导致复合材料在大挠度阶段的弯曲韧性明显减小。

High-performance martensitic stainless steel nanocomposite powder for direct energy deposition prepared by ball milling

Direct energy deposition(DED)has great potential for the production of stainless steel matrix nanocomposite parts.However,the propensity of nanoparticle agglomeration leads to the difficulty in realizing homogenous dispersion of nanoparticles in the matrix.In this study,a series of agglomeration-free nanoWC-Co-reinforced 420 stainless steel matrix nanocomposite powders with high flowability were prepared by ball milling under the optimal parameters.The effect of ball milling time on the properties of the composite powders was investigated.Excellent powder properties ensure the DED processing performance.Furthermore,the corresponding composites were fabricated by DED,and the effects of nano-WC-Co content on the properties of the composites were comprehensively investigated.The contact angles between the single pass cladding layer and the substrate change with increasing nano-WC-Co content(decrease from 127.38°to 113.07°).The different contact angles will significantly influence the quality of the multipass cladding layer.Furthermore,the addition of nanoWC-Co leads not only to further grain refinement but also to more pronounced isotropy of the micros tructure.With the increase in nano-WC-Co content,the corrosion resistance is significantly improved(62.28%lower corrosion current for 420-15 wt%nano-WC-Co than for 420).

Effect of Si content on impact-abrasive wear resistance of Al2O3p/steel composites prepared by squeeze casting

The 40Cr steel matrix composites were reinforced with Al203 particulates （Al2O3p） through Si adding to improve the impact-abrasive wear resistance, in which Si powder ranging up to 25% of the AlzO3p weight was added into the Al2O3p preforms; then, the composites were fabricated by squeeze casting. For all composites, alumina particles are evenly distributed, and Si powder is dissolved in the matrix. Without Si powder addition, the 40Cr steel matrix contains only pearlite; however, ferrite appears and increases with Si powder addition. In the impact-abrasive wear tests, the impact frequency is 80 min^-1 and the impacting energy is 2 J. With increasing Si powder, the wear of the composites first decreases obviously, reaches the minimum at 10% and then increases. The effect of Si addition on the wear resistance can be attributed to two reasons： one is increasing the hardness of the matrix, and the other is improving the interfacial bonding between Al2O3p and steel. The wear mechanism of the composites is abrasive wear when the Si powder is 〈 10 wt%. Otherwise, it is a mixed mode of abrasive and delamination wear.

电冶熔铸WC/钢复合材料中WC的溶解行为

用电冶熔铸工艺制备不同WC含量的WC/钢复合材料,研究了WC颗粒在复合材料钢基体中的溶解行为和影响因素。结果表明:随着WC含量的增加,碳化物从钢基体晶界处分布逐渐转向晶内分布;随着WC颗粒尺寸的增大,在WC颗粒与钢基体界面处形成一层反应物,它阻止了WC颗粒在钢基体中的进一步溶解,同时也提高了两相界面的结合强度。通过调整电冶熔铸工艺参数和WC颗粒的尺寸及含量,可以控制WC颗粒在复合材料中的溶解行为。

碳化钨颗粒增强钢基复合材料的冲蚀磨损性能研究

以直径为188～250um的石英砂为磨料，在自制颗粒冲蚀磨损试验机上对WC颗粒增强ZG45钢基表层复合材料的气-固两相冲蚀磨损性能进行研究，采用扫描电子显微镜观察其磨损表面形貌．结果表明，在相同冲蚀角条件下，增强相WC颗粒的直径越大，复合材料的耐磨性越差，复合材料在冲蚀角为45°时的冲蚀磨损率最大；而ZG45钢在冲蚀角为15°～30°范围内的冲蚀磨损率达到最大值，此后随着冲蚀角增加而减小；复合材料抗冲蚀磨损性能在较小冲蚀角（15°左右）下优于ZG45钢，在较大冲蚀角（≥30°）时劣于ZG45钢．

WC/钢基合金不同热处理状态的微观特征

对ＷＣ／钢基复合材料进行了比较细致的微观分析，揭示了这种材料具有与相近基体成分的钢材明显不同的微观特征。其退火组织典型的”白区”与”暗区”分别由大块硬质相与基体上细小碳化物的密集分布区相间而成。在９６０℃～１１００℃宽范围内加热淬火后均可得到细马氏体组织（奥氏体晶粒度为ＡＳＴＭ１１～１２．５级）。此材料具有大、中、小三种不同尺寸的碳化物分布；大块硬质相中棱角状碳化物与团块状碳化物的性质与物理状态均不相同。本工作还测试分析了合金微观组成单元的显微硬度及与宏观洛氏硬度的对应关系。

原位TiC颗粒增强铸造钢基复合材料制备工艺

利用钢液自身的高温直接引燃压入其中的Ti C Fe预制块 ,原位合成TiC增强颗粒 ,然后 ,对含有TiC颗粒的钢液进行铸造成形 ,即可获得TiC颗粒增强钢基复合材料。着重研究了钢液温度、合成的TiC颗粒含量以及钢液保温时间对复合材料组织的影响。在此基础上 ,优化了复合材料的制备工艺参数 。

颗粒复合材料中硬质相(WC)与钢基体的交互作用及其影响

通过组织观察、微区能谱分析，表明碳化钨增强颗粒复合材料中部分硬质相粒子与钢基体之间存在界面溶解及钨、铁等元素的相互迁移，这也为扩散理论的计算结果所验证。这种硬质相与基体间的交互作用是此类材料的重要特征，并对材料的多种性质与行为产生深刻的影响。

电冶熔铸WC/钢复合材料组织及碳化物演变的研究

采用电冶熔铸法制备了以GCr15轴承钢为基体,WC颗粒为硬质相的WC/钢基复合材料。借助金相分析、扫描电镜、X射线衍射、透射电镜及能谱分析等方法研究了该材料熔铸态显微组织结构及其演变过程。结果表明:随着加入WC含量和颗粒尺寸的不同,其凝固后组织结构不同。当加入10%WC时,WC颗粒大多溶解于钢液中,冷却后沿晶界析出断续网状复式碳化物,同时基体中析出细小的Cr7C3、β-WC1-x、Fe3W3C颗粒;当加入20%WC时,大颗粒WC外围部分溶解形成Fe3W3C反应层,钢基体中析出共晶碳化物;当加入35%WC时,显微组织主要是以γ-Fe+WC、γ-Fe+Fe3W3C共晶组织为主,多数呈树枝状和锚状,少数为不规则块状;当加入40%或50%WC时,WC颗粒基本保留原始形状且稳定不易溶解,多数呈三角状、矩形,均匀分布。

12Cr1MoV钢高温长时加热过程中基体成分的变化

用扫描电镜能谱分析测定了 12Cr1MoV钢高温长时加热后基体 (α相 )内合金元素含量的变化 ,发现当Larson Miller参数从P =2 0 0 0 0到P =2 2 0 0 0变化时 ,Mo含量下降了 2 / 3,Cr与V下降 1/ 3。并且由晶粒中心到晶界存在明显的合金元素浓度分布梯度 ,这些均符合扩散动力学规律。本文还讨论了

TIC颗粒增强钢基表面复合材料的制备

采用Ti—C-Al-Ni系SHS熔铸制备Tic颗粒增强钢基表面复合材料，研究了其组织和耐磨性。结果表明：用SHS熔铸法制备的钢基表面复合材料强化相和基体结合良好；表层TiC颗粒分布密集，颗粒均匀圆整，粒度为1～2μm；表面硬度HV高达950，且硬度由表层向基体呈梯度分布；磨损时密集的高硬度的细小圆球状TiC颗粒大大降低了磨损率；耐磨性比基体提高5．6倍。

WC溶解对WC_p/钢基表层复合材料组织和性能的影响

利用V-EPC法制备了WC颗粒增强钢基表层复合材料。通过金相、扫描电镜、XRD、显微硬度及冲击磨料磨损性能测试等手段重点研究了在预制层中添加镍基自熔合金粉末(Ni6025WC)后,WC在基体中的溶解对复合材料组织和性能的影响。结果表明,WC在复合层中全部溶解使复合层基体中出现珠光体,残留奥氏体,马氏体以及M6C型碳化物,经分析知该M6C型碳化物为Fe3W3C。本试验得到的试样显微硬度与同类WC/钢基表层复合材料相比显著降低,冲击磨料磨损下的体积磨损率也较高。这些均表明WC在基体中过度溶解和Fe3W3C在基体中的含量较多时,复合材料的性能较差。

WC/钢基合金的强韧化因素分析

基于力学性能试验、断裂韧性试验及微观分析 ,对碳化钨增强钢基颗粒复合材料的强化与韧化因素作了较全面的综合分析 ,得出此类材料的主要强韧化机理为高强韧的马氏体、大量超硬碳化物的复合强化、超细晶粒强韧化、界面强韧化以及硬质相与基体交互作用带来的强韧化效果 .

氧化铝颗粒耐热钢基复合材料的高温磨损特性

采用化学气相沉积技术对氧化铝颗粒表面进行涂层处理,通过负压铸渗工艺制备了氧化铝颗粒耐热钢基复合材料,并对其在900℃下的高温磨料磨损特性进行了研究,结果表明:耐热钢在高温下的磨损主要是由磨料的滚压形成的挤出唇、翻边脱落所引起,磨损量较大,而复合材料高温磨损时颗粒突出于基体,承受载荷多,阻碍了磨粒对基体的损伤,因而抗磨性较好,其高温耐磨性是基体材料的33倍多.