Friction and wear properties of TiAl and Ti2AlN/TiAl composites at high temperature

The high-temperature friction and wear properties of TiAl alloys and Ti₂AlN/TiAl composites (TTC) in contact with nickel-based superalloy were studied. The results showed that, at 800 and 1 000 °C, the coefficient of the friction (COF) decreased with the increase of sliding velocity and the wear loss of the TTC decreased with the increase of volume fraction of Ti₂AlN. The wear mechanisms of the pairs are adhesive wear and the wear debris mainly comes from the contacting nickel-based superalloy. The intergranular fracture and the cracking of the phase boundary in the lamellar structure are the wear mode of TiAl alloy. The wear mode of TTC is phase boundary fracture and adhesive spalling. The abrasive resistance of TTC is slightly higher than that of TiAl alloy.     

Wear mechanism for spray deposited Al-Si/SiC_p composites under dry sliding condition

Al-Si/15%SiCp(volume fraction) composites with different silicon contents were fabricated by spray deposition technique, and typical microstructures of these composites were studied by optical microscopy(OM). Dry sliding wear tests were carried out using a block-on-ring wear machine to investigate the effect of applied load range of 10-220 N on the wear and friction behavior of these composites sliding against SAE 52100 grade bearing steel. Scanning electron microscopy(SEM) and energy-dispersive X-ray microanalysis(EDAX) were utilized to examine the morphologies of the worn surfaces in order to observe the wear characteristics and investigate the wear mechanism. The results show that the wear behavior of these composites is dependent on the silicon content in the matrix alloy and the applied load. Al-Si/15%SiCp composites with higher silicon content exhibit better wear resistance in the applied load range. Under lower loads, the major wear mechanisms are oxidation wear and abrasive wear for all tested composites. Under higher loads, severe adhesive wear becomes the main wear mechanisms for Al-7Si/15%SiCp and Al-13Si/15%SiCp composites, while Al-20Si/15%SiCp presents a compound wear mechanism, consisting of oxidation, abrasive wear and adhesion wear.     

Influence of Ta on microstructure and abrasive wear resistance of laser clad NiCrSiB coating

A mixture of NiCrSiB alloy powder and tantalum (Ta) powder was used as laser clad material to improve abrasive wear resistance of the Ni-based coating. The microstructure and wear resistance of the coating were investigated. Addition of Ta element works to suppress the growth of coarse M₇C₃ carbide in the coating, resulting in a decrease in aspect ratio of coarse carbide. In the abrasive wear test, in situ synthesized TaC particles well bond with Ni-based matrix, and are hardly pull out from wear surface. Grooves on the worn surface of NiCrSiB coating are much deeper and sharper than those in the NiCrSiB+Ta composite coating. Also, a weight loss of the composite coating is much lower than that of the NiCrSiB coating. The wear resistance of the laser clad Ni-based coating is enhanced to a much greater extent through the addition of Ta. This is attributed to the in situ synthesized hard TaC particles of nearly equiaxed shape, the Ni-based matrix strengthened by Ta and the decrease in aspect ratio of the coarse brittle carbides.     

Effect of salt spray corrosion on tribological properties of HVOF sprayed NiCr-Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> coating with intermediate layer

The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr₃C₂ coating with intermediate layer. Ni-Zn-Al₂O₃ coatings as interlayers were prepared by low pressure cold spray (LPCS) between NiCr-Cr₃C₂ cermet coatings to form a sandwich structure to enhance the corrosion resistance properties. The tribological properties were examined using the UMT-3 fricition and wear tester by line-contact reciprocating sliding under dry and salt spray one week corrosion. The morphology, element distribution, and phase compositions of the coating and worn sufaces were analyzed by using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction respectively. The corrosion behavior of the coating was studied by the open-circuit potential, the electrochemical impedance spectroscopy, potentiodynamic polarization, and salt spray corrosion methods. It is found that the sandwich structured coating has better corrosion resistance than the single layer coating. The results show that under dry wear conditions, the wear mechanism is abrasive and adhesive wear, whereas under salt spray corrosion conditions it becomes corrosion wear. The friction coefficient of the sandwich structured coating after salt spray corrosion is slightly lower than the dry friction coefficient, but the weight of the wear loss is lower than that under dry condition.     

纳米SiO2填充尼龙PA1010的摩擦磨损性能实验研究

用纳米 Si O2 填充 PA1 0 1 0制备了尼龙复合材料 ,并用 MM- 2 0 0磨损试验机对尼龙复合材料与 45钢在干摩擦条件下的摩擦磨损实验进行了实验 .研究表明 ,纳米 Si O2 填充 PA1 0 1 0大幅度提高了尼龙复合材料的耐磨性 ,降低了摩擦系数 .纳米 Si O2 填充量在 1 0 %左右时 ,尼龙复合材料达到最低摩擦系数 0 .32和最低磨损量 0 .2 mg,磨损量比纯 PA1 0 1 0降低了 60多倍 ,摩擦系数降低了 1倍 .对纳米 Si O2 填充尼龙的磨损机理研究发现 ,纳米 Si O2 填充尼龙复合材料的磨损机理受滑动速度和接触载荷影响比较大 .当摩擦副 PV值小于 60 Nm/ s时 ,尼龙复合材料的磨损机理主要是切削和粘着磨损 .当摩擦副 PV值大于 60 Nm/ s时 ,磨损机理转变为疲劳剥层或熔融流变 ,导致磨损量急剧增长 .     

Surface functionalized carbon nanofibers and their effect on the dispersion and tribological property of epoxy nanocomposites

Surface functionalization of carbon nanofibers (CNFs) was carried out, i e, CNFs were firstly oxidized and then the surface was silanized by 3-Aminopropyltriethoxysilane (APTES) via an assembly method. A new kind of high wear resistance s-CNFs/epoxy composite was fabricated by in-situ reaction. FTIR spectroscopy was used to detect the changes of the functional groups produced by silane on the surface of CNFs. The tribological properties and microstructures of modified and unmodified CNFs/epoxy composites were studied, respectively. The expremental results indicate that APTES is covalently linked to the surface of CNFs successfully and improves the dispersion of CNF in epoxy matrix. The friction coefficients and the wear rates of s-CNFs/epoxy composites are evidently lower than those of u-CNFs/epoxy composites under the same loads. Investigations also indicate that abrasive wear is the main wear mechanism for u-CNFs/epoxy composite, with slight adhesive wear for s-CNFs/epoxy composite under the same sliding wear condition.     

Effect of Carbon Nanotube on the Oscillating Wear Behaviour of Metal-PTFE Multilayer Composites

Two kinds of metal-PTFE multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene(PTFE) filled by carbon nanotubes(CNTs) or not, were prepared. The wear properties of metal-PTFE multilayer composites oscillating against 45 carbon steel under dry condition were evaluated on an oscillating wear tester, and the effect of CNTs on wear behaviour of metal-PTFE multilayer composites was studied. The results showed that the worn surface of metal-PTFE multilayer composites was characterized by adhesive wear, abrasive wear and fatigue wear. The CNTs greatly increased the adhesion strength of PTFE in the metal-PTFE composites and thereby greatly reduced puck, ploughing, and fatigue failure of PTFE during wearing. The PTFE filled with CNTs prevented direct contact between the mating surfaces and served as fine self-lubricating film, in which the oscillating wear mechanism of the composites was changed to a slightly adhesive wear. Therefore, the CNTs significantly decreased the weight loss and obviously increased the wear resistance of metal-PTFE multilayer composites.     

In situ prepared Al-Si alloy matrix composites reinforced by γ-Al2O3p

A γ-Al2O3 particles reinforced Al-Si alloy matrix composite was fabricated by adding NH4Al（SO4）2 to molten aluminum alloy. TEM observation shows that in-situ γ-Al2O3 particles are generally spherical and uniformly distributed in the matrix. The results of dry sliding wear tests show that the wear resistance of the composites increases with increasing mass fraction, and the volume loss is considerably lesser than that of the matrix and is lesser than that of the composites by adding γ-Al2O3 particles directly.     

Microstructural characterization and mechanical property of Fly Ash/Al-25Mg composites

Fly ash/Al-Mg composites are fabricated by powder metallurgical method. The morphology and structure of fly ash/A l-Mg composites are characterized by scanning electron microscope （SEM） and X-ray diffraction, respectively. The influences of different fly ash content on the friction and wear behavior of the composites are investigated at a constant sliding velocity of 400 r/min and the worn mechanism of composites is discussed. The results indicate that the friction coefficient is steadily lower than that of Al alloy matrix at the lower fly ash content and loads. For the fly ash/Al-Mg composites, the wear mechanism is characterized as abrasive wear and adhesive wear under small normal load and at low fly ash content, and it is characterized as delamination wear and abrasive wear transferred onto the counterpart under high normal load and at high fly ash content.     

Tribological properties of self-lubricating laminated ceramic materials

In order to improve the tribological properties of ceramic composites, Al2O3/TiC-Al2O3/ TiC/CaF2 self-lubricating laminated ceramic composites were prepared by vacuum hot pressing sintering. Experiments were conducted to get mechanical properties and the friction and wear properties were also measured with friction and wear tester. The worn surfaces were observed by scanning electron microscope （SEM） and energy dispersion spectrum （EDS）. The wear resistance properties and the self-lubricating effect of ceramic composites were analyzed. Results show that the Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites layers are well-defined with a higher bonding strength and the mechanical performances are uniform enough to overcome the anisotropy of weak laminated ceramic composites. In addition, the fracture toughness of Al2O3/TiC layers is also improved. Its friction coefficient and wear rates decrease with the increase of rotation speed and load. Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites have good wear resistance because of the tribofilm formed by the CaF2 solid lubricants. The wear mechanisms of Al2O3/TiC/ CaF2 layers are abrasive wear and Al2O3/TiC layers are adhesive wear.     

填料改性UHMWPE基复合材料拉伸磨损性能的研究

研究了填料颗粒改性的超高分子量聚乙烯（ＵＨＭＷＰＥ）体系的拉伸与磨损性能。加入少量的粉煤灰（＜１０％）和ＳｉＣ（３０％）可提高体系的拉伸强度，并且颗粒越细小，越有利于拉伸强度的提高。ＳｉＣ，Ａｌ２Ｏ３，特别是４０目石英砂可大幅度提高（约４～６倍）体系的耐磨料磨损能力。试验结果表明，载荷Ｐ是影响ＵＨＭＷＰＥ体系磨损率的重要因素。载荷越大，磨损率越高，而与相对摩擦速度ｖ关系不大。所得结果为减粘耐磨复合材料的仿生设计提供了可靠的依据     

GF/MoS2改性PTFE密封唇片材料的力学及摩擦学性能

采用玻璃纤维(GF)微粉与MoS₂复合改性聚四氟乙烯(PTFE)密封唇片材料,考察复合材料的力学、干摩擦磨损性能及其磨损机理。结果表明:当GF质量分数为15%时,PTFE/GF试样的回弹率达到最大值92.5%,摩擦因数为0.29,相比纯PTFE有所增加,而磨损率大大降低,仅为1.8×10?6mm3/(N·m);在此基础上,当MoS₂添加量为5%时,PTFE/GF/MoS₂试样的回弹率略有降低,但仍然保持在90%以上,其摩擦因数为0.31,体积磨损率进一步降低到1.25×10?6mm3/(N·m)。磨损面SEM分析表明:纯PTFE呈现出严重的塑性变形和粘着磨损特征,而PTFE/GF主要表现为磨粒磨损行为;适当MoS₂含量的PTFE/GF/MoS₂试样在摩擦过程中磨粒磨损特征消失,仅有非常轻微的粘着磨损行为。     

Wear behavior of Cu matrix composites reinforced with mixture of carbon and carbon nanotubes

In order to improve wear resistance and decrease the cost, carbon and carbon nanotubes reinforced copper matrix composites were fabricated by the power metallurgy method. The effects of carbon (carbon and carbon nanotubes) volume fraction and applied load on the friction coefficient and wear rate under dry sliding of the composites were investigated at room temperature. By scanning electron microscopy (SEM), the worn surfaces and debris were observed, and wear mechanism was also analyzed and discussed. The experimental wear process consists of the run-in, steady wear and severe wear process with the increasing of sliding distance. Both the friction coefficient and wear rate of the composites first decrease and then increase with the increasing of carbon volume fraction. The minimum friction coefficient and wear rate are obtained when carbon is 4.0vol%. The wear mechanisms of the composites change from the adhesive wear and delamination wear to abrasive wear with the increasing of carbon volume fraction. Funded by the National Natural Science Foundation of China (50873047) and the Natural Science Foundation of Gansu Province (3ZS061-A25-039)     

一种适合硬膜抗磨粒磨损性能试验方法的研究

提出了一种适合评估硬膜材料抗磨粒磨损性能试验的新方法 ,并研究了各种因素对硬膜抗磨粒磨损试验结果的影响。试验发现 ,硬膜的磨损量与磨损时间以及试棒转速成正比 ;当磨料粒度在一定的范围内变化时 ,磨损量与磨料的粒度成正比 ;当磨料的粒度超过某一临界尺寸后 ,磨损速度变化不大。在粒度为 1 80目时 ,磨损试验的效果最佳。在有饱和水溶液的磨料中 ,同时存在着磨料磨损和气蚀磨损两种磨损方式。     

Effect of Cu-Ti-C reaction composition on reinforcing particles size of TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Cu composites

TiC _x /Cu composites were fabricated by combustion synthesis and hot press technology. Using XRD, SEM, EDS, FESEM analysis methods, the effects of various carbon sources and different Cu contents on the microstructures of TiC _x /Cu composites and the size of TiC _x particles were investigated. Results showed that TiC _x reinforcing particles size increases with decreasing Cu content in Cu-Ti-C reaction system. With carbon nanotubes (carbon black) serving as carbon source, the generated TiC _x particles size transits from nanometer to submicron when Cu content corresponding to the reaction system is reduced to 60 vol% (70 vol%); while graphite serves as carbon source, there is no clear limiting concentration. C particles with smaller size, larger specific surface area and better distribution result in finer TiC _x particles, which is more beneficial to generating nano-sized TiC _x /Cu composites.     

Biodegradation and mechanical property of polylactic acid/thermoplastic starch blends with poly (ethylene glycol)

The effects of adding poly (ethylene glycol) (PEG) into polylactic acid/thermoplastic starch blends (PLA/TPS) on the properties were investigated by DSC, SEM and mechanical property-testing. The blends of PLA/TPS blended with increasing content PEG exhibited lower temperature of glass transition (Tg) and lower temperature of melting (Tm) as well as higher melt flow index (MFI), which indicates the plasticization and processability of the composites were dramatically improved. The tensile strength, flexural strength and izod impact strength of PLA/TPS (80/20) increased at first and then decreased with increasing content of PEG due to stronger interfacial adhesion. The optimized mechanical property can be obtained for the blend with 3 wt% PEG. The samples containing PEG after soil burial for 5 months showed quicker degradation being accompanied with large weight loss and mechanical properties loss.     

Microstructure and Tribological Behavior of Al_2O_3 Particle Reinforced Al Matrix Composites Fabricated by Spark Plasma Sintering

Nanoparticles and microparticles reinforced Al matrix composites were fabricated by spark plasma sintering, and the microstructure and tribological properties were investigated systemically. The nano-Al_2O_3 particle and micro-Al_2O_3 particle uniformly dispersed in Al matrix composites. The introduction of nanoparticles is beneficial to the decrease of friction coefficient and wear rate, while microparticles are responsible to the high friction coefficient, resulting in the abrasive wear. With the introduction of both nanoparticles and microparticles, their synergic effect will lead to the variation of tribological behavior.     

Preparation, characterizations and magnetic properties of doped barium hexaferrites BaFe12-2x Mn x Sn x O19 (x = 0.0–1.0)

A series of doped barium hexaferrites BaFe12-2xMnxSnxO19 (x = 0.0-1.0) particles were prepared by the co-precipitation/molten salt method. The particle size and crystalline of the samples BaFe12-2xMnxSnxO19 decrease with an increase in the doping amount x. When x is less than 0.8, the pure BaFe12-2xMnxSnxO19 particles with hexagonal plate morphology are obtained. The effects of substitution on magnetic properties were evaluated and compared to nomal BaFe12O19. The specific magnetizations (Ms) of doped materials have been significantly improved. Among all these compositions, the BaFe10.4Mn0.8Sn0.8O19 sample has the highest Ms value of 81.8 A?m2?kg-1 at room temperature and its intrinsic coercivity (Hc) is 44.5 kA?m-1. The as-prepared doped barium ferrites exhibit a low temperature coefficient of coercivity close to zero. The coercivity is independent of temperature when x is in the a range 0.5-0.7.     

热压多晶SiC 陶瓷的原位摩擦和磨损

利用场发射扫描电子显微镜（ＦＥ－ＳＥＭ）中的销－盘式滑动摩擦磨损装置对热压多晶ＳｉＣ陶瓷在真空中的摩擦和磨损行为进行了原位观察和分析,发现随着磨损圈数的增加其摩擦系数逐步增大,磨痕深度也不断增加,其磨损机理主要为脆性微性微切削和沿晶裂纹造成的剥落。     

The Dielectric Properties and Preparation Method of BaTiO3/PVDF 0-3 Composites

A series of 0-3 composties of the polyvinylidene fluoride (PVDF) and BaTiO3 was prepared,BaTiO3 was modified with titanate coupling agent .The dielectric properties and the interfacial interaction of composites by different preparation methods were examined and compared,The result shows that the relaive dielectric constant ε of the composite prepared in solution has a maximum value at about 70% weight fraction of BaTiO3 and the dielectric loss tanδ increases rapidly when the fraction exceeds 70%, For the composite preared in melt, the relative dielectric constant ε almost raches a maximum value at about 60% weght fraction of BaTiO3 and the dielectric loss is comparatively lower,The deielectric proerties of composites ore improved by using a coupling aent.