Antifriction properties of some composite sintered packing materials. II

Summary The addition of more than 20 vol.% of solid lubricants to the materials investigated is undesirable, because it adversely affects their strength properties and increases their coefficients of friction and specific wear, with increasing rubbing velocity and pressure, high temperatures are generated in the friction surface zone, resulting in the oxidation of the solid lubricant and the metallic matrix of the materials and formation of oxides on the surface. The presence of oxides on the friction contact surface inhibits the propagation of thermal seizure processes, in consequence of which specific wear and the coefficients of friction decrease. Conversely, the burning out of graphite solid lubricant is responsible for the deterioration of the antifriction properties of materials. As a result of this, with increase in rubbing velocity, the coefficients of friction and specific wear of materials with additions of chemically stable solid lubricants decrease, while those of nickel-graphite materials increase.On the basis of the investigations described, natural mica (phlogopite) and boron nitride may be recommended as substitutes for graphite as solid lubricants in packing materials. From the point of view of operation in packing elements of gas-turbine engines, the best combination of antifriction properties is offered by sintered composite nickel-mica and 20Cr-80Ni alloy—boron nitride materials.Translated from Poroshkovaya Metallurgiya, No.9(45), pp. 61–66, September, 1966.     

Transient thermal analysis of solidification in a centrifugal casting for composite materials containing particle segregation

One-dimensional heat-transfer analysis during centrifugal casting of aluminum alloy and copper base metal matrix composites containing Al₂O₃, SiC_p, and graphite particles has been studied. The model of the particle segregation is calculated by varying the volume fraction during centrifugal casting, and a finite difference technique has been adopted. The results indicate that the thickness of the region in which dispersed particles are segregated due to the centrifugal force is strongly influenced by the speed of rotation of the mold, the solidification time, and the density difference between the base alloy and the reinforcement. In the case where the base alloy density is larger than that of the particles, the thickness of the particle-rich region near the inner periphery decreases with an increase in speed, thereby increasing the volume fraction of dispersion. The solidification time of the casting is also dependent upon the speed of rotation of the mold, and it decreases with an increase in speed. This study also indicates that the presence of particles increases the solidification time of the casting.     

铜包铝复合棒充芯连铸设备的开发

为了实现以铝代铜,开发铜铝复合材料,设计和制造了一台制备铜包铝复合棒坯的充芯连铸试验机.该机器的特点为:结晶器为水冷铜套内衬石墨套;在高度方向上设置一高一低直径不同的加热器,下加热器与结晶器相连接在此试验机上;充芯与连铸同时进行.利用该设备,成功地连铸出芯部直径为φ24mm,外层厚度为8mm的铜包铝双金属复合棒.     

Particle fracture, retention, and fluid flow in metal matrix composite friction joints

Friction joining of metal matrix composite (MMC)/MMC and MMC/AISI 304 stainless steel base materials is examined using a combination of experimental testing and numerical modeling. In particular, the fracture of reinforcing particles during the friction-joining operation is investigated. The particle diameter and interparticle spacing decrease and the area fraction of particles markedly increases in material immediately adjacent to the bondline. Smaller particles are observed in frictionwelded joints produced using high friction pressures. The principal effect of the forging operation is in decreasing the interparticle spacing. There was excellent correspondence between predicted fluid flow in A1/A1 joints and experimental test results examining the transfer of Al₂O₃ particles during the alloy 6061/alloy 6061 friction-joining operation. It is suggested that small-diameter particles formed due to fracture early in the friction-joining operation are retained at the bondline of MMC/MMC joints as a direct consequence of the flow of plasticized material and reinforcing particles in the contact zone. A combination of numerical modeling of fluid flow and direct experimental testing have confirmed that Al₂O₃ particles transfer from the stationary to the rotating boundary in MMC/MMC friction joints. Also, limit cycles embedded within the flow favor the retention of smalldiameter fractured particles at the bondline of MMC/MMC joints. A quite different situation exists in dissimilar MMC/AISI 304 stainless steel joining. In dissimilar joints, a dynamically quiescent region is formed immediately adjacent to the stainless steel boundary. It is suggested that the absence of flow of plasticized material promotes retention of fractured alumina particles in dissimilar joints.     

Tribotechnical characteristics of powder composite materials based on copper in high-speed friction

Conclusions Copper and the composite materials based on copper (with mullite, glass ceramic, and also sulfur and molybdenum sulfide) have a high friction coefficient (0.23–0.46), a medium temperature of the friction surface (130–270°C), and are susceptible to bonding with the contacting surface (07Khl6N6 steel).The materials containing 10% graphite, sulfur, and molybdenum disulfide have a low friction coefficient (0.09–0.15), do not bond to 07Khl6N6 steel, and can be recommended for service in high-speed friction units.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 52–56, July, 1986.     

贝氏体离心复合轧辊铸造工艺

贝氏体离心复合轧辊由于辊身工作层和芯部采用不同的铸造工艺,具有较高的性价比,是目前广泛应用的冶金轧辊之一.要获得高质量的贝氏体离心复合轧辊,铸造工艺尤为重要.     

摩擦组元对粉末冶金摩擦材料摩擦性能的影响

实验研究了不同种类摩擦组元对粉末冶金摩擦材料摩擦磨损性能的影响。结果表明摩擦组元的显微硬度对摩擦因数和摩擦因数稳定度影响显著。随着摩擦组元显微硬度的提高，摩擦材料的耐磨性提高，而对偶材料的磨损量增大；摩擦材料的表观硬度主要取决于基体组元，摩擦组元的显微硬度对其影响不人。单独依靠一种摩擦组元不能使摩擦材料取得较佳的摩擦性能，综合使用几种摩擦组元，才能得到满意的效果。     

基于神经网络的树脂基摩擦材料摩擦因数的预测模型

为了预测不同成分的树脂基摩擦材料的摩擦性能，建立了摩擦材料成分与摩擦因数之间的人工神经网络（ANN）预测模型。用收集到的30种不同组分的摩擦材料在100℃时的摩擦因数数据作为训练样本对网络进行训练，然后进行拟合，结果表明，网络拟合值与实验数据吻合很好。最后利用该模型对不同成分的4种摩擦材料进行摩擦因数的预测，并研究单一成分对树脂基摩擦材料因数的影响。结果表明，预测值与实测数据基本相符，100℃时预测的摩擦因数最小值μmin.p。与实验中实测的摩擦因数最小值μmin.m的相对误差小于13％，相应的摩擦因数最大值μmin.p与μmin.m的相对误差小于9％。     

Antifriction properties of boron nitride during dry friction in gaseous media and at low temperatures

Summary The article presents the results of an experimental study of the dry friction of boron nitride in gaseous environments and at low temperatures. It is shown that the environment exerts a substantial influence on the wear of boron nitride. Experimental data are given on the wear of boron nitride rubbing against hard nitrided 1Kh18N9T steel in gaseous enviroments (air, argon, nitrogen, and helium) and at liquid nitrogen temperature.Translated from Poroshkovaya Metallurgiya, No. 7 (43), pp. 49–52, July, 1966.     

一种高性能烧结摩擦材料摩擦剂的选择

研究了SiO_2,SiC,B_4C对金属基烧结摩擦材料物理机械性能,特别是摩擦磨损性能的影响。结果表明,同时添加SiO_2,SiC,B_4C作摩擦剂的材料比单独添加SiO_2或SiC,或同时添加SiO_2和SiC的材料综合性能优良。     

Antifriction characteristics of materials produced by dynamic hot pressing (DHP)

Conclusions An investigation was carried out into the wear behavior of a collar-ring frictional pair and into the effects of lubrication, operating conditions, and structure and chemical composition of the ring on the antifriction characteristics of the pair. As iron-graphite and iron-copper-graphite materials produced by the DHP process developed by the authors possess excellent antifriction characteristics, they can be used for collar rings in rubber-metal frictional pairs. With the optimum material composition proposed (5% C + 5% Cu + Fe), the wear resistance of a pair is one and a half to two times higher than that obtained with type 45 steel (without lubrication) and the running-in time is 15–30 min as against 60–90 min with type 45 steel.Translated from Poroshkovaya Metallurgiya, No. 12(216), pp. 60–65, December, 1980.