表面硅颗粒整形对高硅铝合金缸套摩擦磨损性能的影响

研究了一种新型的高硅铝合金缸套表面处理技术,采用橡胶圈+金刚石颗粒的方式研磨缸套表面,这种表面硅颗粒整形技术可以使硅颗粒凸出表面并且边角圆化。整形处理缸套表面2 min,可制备出凸出高度约为1.2μm,边角轮廓自然圆化过渡的硅颗粒。摩擦磨损试验结果表明,相对于未整形,整形处理后的高硅铝合金缸套的摩擦因数可从0.14降低到0.12,降幅约为14%;磨损量从0.7 mg降低到0.2 mg,降幅约为71%。未整形的硅颗粒表面覆盖一层铝,或与缸套表面保持同一高度。当活塞环与缸套对磨时,铝作为软金属易发生塑性流变,被碾压覆盖到硅颗粒表面上,发生黏着磨损,所以摩擦因数及磨损量较大。而整形后的硅颗粒凸出缸套表面以承担载荷,加强了表面支承力,而且与铝基体共同形成的凹陷处储油,增大润滑效果,同时其边角圆化,避免了应力集中。所以整形技术可以有效地降低高硅铝合金缸套的摩擦因数及磨损量,改善摩擦磨损性能。     

陶瓷颗粒含量对Cr-Al_2O_3复合镀活塞环摩擦磨损性能的影响

为了研究陶瓷颗粒含量对Cr-Al_2O_3复合镀活塞环摩擦磨损性能的影响,采用镀铬活塞环和4种Al_2O_3陶瓷颗粒含量不同的Cr-Al_2O_3活塞环与CuNiCr合金铸铁缸套组成配对副,对其进行摩擦磨损试验,对比各配对副摩擦因数及磨损量。结果表明,镀铬活塞环-缸套配对副摩擦因数较大,约为其它4种含Al_2O_3陶瓷颗粒的Cr-Al_2O_3活塞环-缸套配对副的1.2倍,磨损也比其它4种配对副严重,摩擦副的表面均已经发生严重的粘着磨损现象;其它4种含陶瓷颗粒的Cr-Al_2O_3活塞环-缸套配对副的摩擦因数相近,缸套的磨损量也相近,活塞环的磨损量随着陶瓷含量的增加而先减小后增加。陶瓷颗粒的镶嵌提高了活塞环的耐磨性能,陶瓷含量过少,活塞环表面承载能力不足;陶瓷颗粒含量过多,陶瓷颗粒易脱落,这些都会增大活塞环的磨损量。     

重型车辆发动机电镀Cr活塞环的摩擦学性能

利用SRV试验机模拟重型车辆发动机电镀Cr活塞环/缸套摩擦副的工作状态,测试了不同条件下摩擦副的摩擦因数和磨损量.采用扫描电镜(SEM)、能谱仪(EDS)分析了磨痕形貌和表面化学成分,研究了电镀Cr活塞环的磨损机制.结果表明,随载荷的增加,摩擦副的摩擦因数减小,总失重量增加.随滑动频率的增加,摩擦副的摩擦因数减小,总失重量先减小后增加,滑动频率为20 Hz时,总失重量达到最小值.随温度的升高,摩擦副的摩擦因数增大,总失重量增加.活塞环和缸套的磨损机理以磨粒磨损为主,在高载荷,高频率或高温条件下,活塞环的磨损机理转变为磨粒磨损和黏着磨损.     

激光光整对高硅铝合金缸套材料摩擦磨损性能的影响

切取高硅铝合金缸套试样,并对工作面进行激光光整,研究其对摩擦磨损性能的影响。结果表明,激光扫描速度为600 mm/min,离焦量2 mm,功率为1 000 W时硅颗粒最大凸出高度为1.243μm,与未处理试样相比,摩擦因数从0.141降到0.113,降幅达19.9%,磨损量从0.7 mg降到0.2 mg,降幅达71.4%;激光光整使高硅铝合金缸套工作面上的硅颗粒凸出且边角圆化,硅颗粒的凸出,避免了铝基体与活塞环的直接接触,并增大了储油润滑的效果,减少了粘着磨损的风险,也降低了摩擦力,从而改善了高硅铝合金缸套材料的摩擦磨损性能。     

微坑分布位置对复合润滑结构缸套摩擦磨损性能的影响规律

采用电火花加工方法在FeNi合金镀铁缸套试样表面的止点、中点、全程位置刻蚀微坑织构,采用球磨法对微坑填充固体润滑剂MoS_2以制备复合润滑结构缸套。采用对置往复式摩擦磨损试验机,研究微坑分布位置对复合润滑结构缸套摩擦磨损性能的影响规律。采用SEM和EDS研究配副的磨损形貌。结果表明:复合润滑结构缸套能提高承载性能、降低摩擦因数,但不一定都能提高缸套的磨损性能和抗拉缸性能。唯有微坑分布在止点的复合润滑结构缸套相比未处理缸套,表现出良好的减摩耐磨和抗拉缸性能,摩擦因数降低了4.97%~6.26%,对磨环磨损量减少了58.3%,拉缸时间延长了10倍。随着往复运动的进行,微坑中的MoS_2逐渐向缸套表面转移,改善了止点区域的润滑性能,良好保护了摩擦界面。     

缸套内壁激光渗硫复合层的组织与抗高温磨损性能

针对大功率密度柴油机缸套高温磨损失效问题,利用低温离子渗硫技术在42MnCr52钢激光淬火表面制备了渗硫层,采用扫描电子显微镜(SEM)、X射线衍射(XRD)、纳米硬度仪、划痕仪和台架试验装置分析了复合层的形貌组成、组织结构、力学性能与高温磨损性能。结果表明,复合层表面疏松多孔,其相组成主要为FeS,厚度约为5μm,与基底结合紧密。在发动机台架试验条件下,激光渗硫复合处理能降低缸套的磨损量,同时减轻了对磨活塞环的磨损,其主要原因是复合层表面的固体润滑硫化物有效抑制了高温粘着磨损和磨粒磨损,改善了缸套/活塞环摩擦副表面的匹配性能,使缸套的抗高温磨损性能得到提高。     

FeNi合金镀铁缸套的摩擦磨损性能

采用对置往复式摩擦磨损试验机,选用CKS活塞环为配副,以摩擦因数、磨损量、断油摩擦时间为表征参数,以BP合金铸铁缸套为参照对象研究FeNi合金镀铁缸套的摩擦磨损性能,探索FeNi合金镀铁缸套的磨损机制。逐级加载的磨损试验表明:FeNi合金镀铁缸套的摩擦因数较BP合金铸铁缸套增大11%~20%;而磨损量则降低了11%;贫油试验表明两种缸套拉缸时间均随载荷增大而缩短,在40 MPa时FeNi合金镀铁缸套的拉缸时间较BP合金铸铁缸套延长了约6.5倍。与BP合金铸铁缸套的磨损机理为基体碾压平台在反复接触应力作用下脱落,以及犁削/切削形式的磨粒磨损不同,FeNi合金镀铁缸套的磨损机理主要是网状裂纹周围镀铁层的疲劳剥落。     

激光强化铸铁活塞环的磨损性能

为降低活塞环、缸套摩擦副的磨损和改善配副性,采用激光熔覆和电镀技术在球墨铸铁表面分别制备原位析出颗粒增强金属基复合材料表层和镀铬层。分别以激光熔覆和镀铬强化的球墨铸铁为上试样,灰铸铁为下试样,模拟活塞环和缸套的工作环境,进行SRV快速磨损实验。实验结果表明:镀铬活塞环和灰铸铁缸套配副,摩擦系数在0.117 0~0.133 2范围内变化,且随摩擦时间的延长,摩擦系数逐渐增加,其磨损机制为粘着磨损;在相同的工艺条件下,激光熔覆强化的活塞环与灰铸铁配副,摩擦系数在0.067~0.085范围内变化,随摩擦时间的延长逐渐降低,其磨损机制为微切削。     

不同角度凹槽织构对缸套-活塞环摩擦性能的影响

针对船舶柴油机的缸套-活塞环表面纹理结构的磨损控制问题,利用化学刻蚀技术在缸套表面加工出三种倾斜角的凹槽织构。在MWF-10摩擦磨损试验机上开展织构化缸套试样在不同载荷下的摩擦磨损试验。综合摩擦系数、接触电阻以及磨损表面形貌等来分析不同倾斜角的凹槽织构对其摩擦性能的影响。结果表明:在400 N载荷下,倾角α=60°的凹槽织构对其摩擦系数降低最为明显;在200、600 N的载荷下,倾角α=30°凹槽织构的摩擦系数小。     

CKS活塞环表面微织构几何形貌及排布方式对摩擦学性能的影响

以CKS(铬基陶瓷复合镀)活塞环-硼磷合金铸铁气缸套摩擦副为对象,采用Nd-YAG激光器在CKS活塞环上进行微织构化处理,在对置往复式摩擦磨损试验机上进行摩擦学试验,研究激光微织构几何形貌及排布方式对摩擦副减摩耐磨的作用。采用激光共聚焦扫描显微镜利用台阶法测量磨损量,采用扫描电子显微镜观察样品表面磨损形貌。发现当织构深度30μm、直径130μm、排布角度0°、面积占有率5%时,摩擦副获得最佳的摩擦磨损性能,摩擦因数最低可达0.086,与未织构化的摩擦配副相比,摩擦因数降低约0.013,降低约13%;活塞环磨损率下降约41%,气缸套磨损率下降约46%。活塞环表面微织构可改善摩擦磨损性能的作用机制为,微织构具有储存润滑油、收集磨屑以及减小摩擦副接触面积的作用。     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.     

Microstructures and Mechanical Properties of a Newly Developed Austenitic Heat Resistant Steel

The effect of heat treatment on the microstructures and mechanical properties of a newly developed austenitic heat resistant steel(named as T8 alloy) for ultra-supercritical applications have been studied. Results show that the main phases in the alloy after solution treatment are γ and primary MX. Subsequent aging treatment causes the precipitation of M_(23)C_6 carbides along the grain boundaries and a small number of nanoscale MX inside the grains. In addition, with increasing the aging temperature and time, the morphology of M_(23)C_6 carbides changes from semi-continuous chain to continuous network.Compared with a commercial HR3C alloy, T8 alloy has comparable tensile strength, but higher stress rupture strength. The dominant cracking mechanism of the alloy during tensile test at room temperature is transgranular, while at high temperature, intergranular cracking becomes the main cracking mode, which may be caused by the precipitation of continuous M_(23)C_6 carbides along the grain boundaries. Typical intergranular cracking is the dominant cracking mode of the alloy at all stress rupture tests.     

The 15th Global Foundry Sourcing Conference 2014held in Qingdao China

Organized by Suppliers China Co., Ltd and co-organized by the National Technical Committee 54 on Foundry of Standardization Administration of China, the 15th Global Foundry Sourcing Conference 2014 （hereinafter referred to as FSC 2014） was successfully held on Sep. 23rd in Grand Regency Hotel, Qingdao. More than 500 delegates from home and abroad attended this conference, including over 130 purchasers from 20 countries and 380 domestic and foreign suppliers.     

LASER CLADDED TiCN COATINGS ON THE SURFACE OF TITANIUM

Laser cladded coatings of TiCN were produced on the surface of titanium. To obtain the optimal techniques, several conditions were tested by varying the laser scanning rate. The choice of shielding gas was also studied. The cladded coatings were then evaluated from the surface mechanics point of view based on their microhardness. The microstructure of some interesting samples was investigated by optical micrographs (OM). The results showed that under the condition of fixed pulse frequency and pulse width, the laser scanning rate and the shielding gas are the main factors influencing the components of coatings. TiCN coatings were decompounded and oxidized during the cladding process in the condition of no shielding gas of N2. X-ray diffraction results indicated that the composite coatings composed of TiCN, TiC, Ti2N, and TiO2 were produced using appropriate techniques. The results indicated that the best condition in terms of the surface microhardness is obtained when the scanning rate is 1.5mm / s, the pulse frequency is 15Hz, the pulse width is 3.0ms, and N2 is chosen as the shielding gas. The microhardness of the composite coatings is about 1331kg · mm - 2, which is about 4 times that of the substrate. The optical micrographs indicated that the cladding zone is made up of TiCN, TiO2, and some interdendritic Ti, but the diffusion zone mainly consists of the dendrites phase, and the cladded depth is about 80m, which is more than 2 times that of the laser nitrided sample. There were no microcracks or air bubbles in the cladded sample, which was cladded using the above optimal techniques.     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

INFLUENCE OF HEAT TREATMENT ON DAMPING BEHAVIOUR OF THE MAGNESIUM WROUGHT ALLOY AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Microstructure and Mechanical Properties of X80 Pipeline Steel Joints by Friction Stir Welding Under Various Cooling Conditions

X80 pipeline steel plates were friction stir welded(FSW) under air, water, liquid CO_2 + water, and liquid CO_2 cooling conditions, producing defect-free welds. The microstructural evolution and mechanical properties of these FSW joints were studied. Coarse granular bainite was observed in the nugget zone(NZ) under air cooling, and lath bainite and lath martensite increased signifi cantly as the cooling medium temperature reduced. In particular, under the liquid CO_2 cooling condition, a dual phase structure of lath martensite and fi ne ferrite appeared in the NZ. Compared to the case under air cooling, a strong shear texture was identifi ed in the NZs under other rapid cooling conditions, because the partial deformation at elevated temperature was retained through higher cooling rates. Under liquid CO_2 cooling, the highest transverse tensile strength and elongation of the joint reached 92% and 82% of those of the basal metal(BM), respectively, due to the weak tempering softening. A maximum impact energy of up to 93% of that of the BM was obtained in the NZ under liquid CO_2 cooling, which was attributed to the operation of the dual phase of lath martensite and fi ne ferrite.     

INDUSTRY NEWS

China Securities News reported on March 21, 2014： Guangdong Hongtu Wuhan Die Casting Co., Ltd. （Wuhan Hongtu）, a wholly owned subsidiary of Guangdong Hongtu Technology （Holdings） Co., Ltd., held a groundbreaking ceremony recently. With the registered capital of 50 million Yuan, Wuhan Hongtu has a total land area of 100,000 square meters and a plant construction area of 72,000 square meters. It is expected to have a production capacity of about 30,000 tonnes of aluminum castings annually after it is put into production.     

GROWTH MORPHOLOGIES OF A BINARY ALLOY WITH LOW ANISOTROPY IN DIRECTIONAL SOLIDIFICATION

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.