Effect of Ni content on the wear behavior of Al-Si-Cu-Mg-Ni/SiC particles composites

In recent years,the addition of Ni has been widely acknowledged to be capable of enhancing the mechanical properties of Al-Si alloys.However,the effect of Ni on the wear behaviors of Al-Si alloys and Al matrix composites,particularly at elevated temperat-ures,remains an understudied area.In this study,Al-Si-Cu-Mg-Ni/20wt%SiC particles(SiCp)composites with varying Ni contents were prepared by using a semisolid stir casting method.The effect of Ni content on the dry sliding wear behavior of the prepared compos-ites was investigated through sliding tests at 25 and 350℃.Results indicated that theθ-Al_(2)Cu phase gradually diminished and eventually disappeared as the Ni content increased from 0wt%to 3wt%.This change was accompanied by the formation and increase inδ-Al_(3)CuNi andε-Al_(3)Ni phases in microstructures.The hardness and ultimate tensile strength of the as-cast composites improved,and the wear rates of the composites decreased from 5.29×10^(−4)to 1.94×10^(−4)mm^(3)/(N∙m)at 25℃and from 20.2×10^(−4)to 7×10^(−4)mm^(3)/(N∙m)at 350℃with the increase in Ni content from 0wt%to 2wt%.The enhancement in performance was due to the presence of strengthening network structures and additional Ni-containing phases in the composites.However,the wear rate of the 3Ni composite was approximately two times higher than that of the 2Ni composite due to the fracture and debonding of theε-Al_(3)Ni phase.Abrasive wear,delamination wear,and oxidation wear were the predominant wear mechanisms of the investigated composites at 25℃,whereas delamination wear and oxid-ation wear were dominant during sliding at 350℃.

Damping properties and mechanism of aluminum matrix composites reinforced with glass cenospheres

The damping properties were improved by preparing Al matrix composites reinforced with glass cenospheres through the pressure infiltration method.Transmission electron microscopy and scanning electron microscopy were employed to characterize the microstructure of the composites.The low-frequency damping properties were examined by using a dynamic mechanical thermal analyzer,aiming at exploring the changing trend of damping capacity with strain,temperature,and frequency.The findings demonstrated that the damping value rose as temperature and strain increased,with a maximum value of 0.15.Additionally,the damping value decreased when the frequency increased.Dislocation damping under strain and interfacial damping under temperature served as the two primary damping mechanisms.The increase in the density of dislocation strong pinning points following heat treatment reduced the damping value,which was attributed to the heat treatment enhancement of the interfacial bonding force of the composites.

Microstructure,interfacial reaction behavior,and mechanical properties of Ti_(3)AlC_(2)reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti_(3)AlC_(2)at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated.The results show that the addition of3.0 wt.%Ti_(3)AlC_(2)refines the average grain size ofα(Al)in the composite by 50.1%compared to Al6061 alloy.Morphological analyses indicate that an in-situ Al_(3Ti)transition layer of-180 nm in thickness is generated around the edge of Ti_(3)AlC_(2)at 720℃,forming a well-bonded Al-Al_(3Ti)interface.At this processing temperature,the ultimate tensile strength of A16061-3.0 wt.%Ti_(3)AlC_(2)composite is 199.2 MPa,an improvement of 41.5%over the Al6061 matrix.Mechanism analyses further elucidate that 720℃is favourable for forming the nano-sized transition layer at the Ti_(3)AlC_(2)edges.And,the thermal mismatch strengthening plays a dominant role in this state,with a strengthening contribution of about 74.8%.

Microstructure evolution,mechanical properties and fracture behavior of Al-xSi/AZ91D bimetallic composites prepared by a compound casting

In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically.The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer(MRL),whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites,while the hypereutectic Al-Si/AZ91D composites were opposite.The MRL included eutectic layer(E layer),intermetallic compound layer(IMC layer)and transition region layer(T layer).In the IMC layer,the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg_(2)Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites.Besides,increasing Si content,the thickness proportion of the T layer increased,forming an inconsistent preferred orientation of the MRL.The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content,and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa,which was 73.4% higher than the Al-6Si/AZ91D composite.The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content.The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg_(2)Si particle reinforcement,the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.

Effect of Rare Earths on Tribological Properties of Carbon Fibers Reinforced PTFE Composites

Carbon fibers （CF） were surface treated with air-oxidation and rare earths （RE）, respectively. The effect of RE surface treatment on tensile strength and tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites was invest/gated. Experimental results revealed that RE was superior to air ox/dation in improving the tensile strength, elongation, and the tensile modulus of CF reinforced PTFE （CF/PTFE） composite. Compared to the untreated and air-oxidated CF/PTFE composite, the RE treated composite had the lowest friction coefficient and specific wear rate under a given applied load and reciprocating sliding frequency. The RE treatment effectively improved the interfacial adhesion between CF and PTFE. With strong interfacial coupling, the carbon fibers carried most of the load, and direct contact and adhesion between PTFE and the counterpart were reduced, accordingly the friction and wear properties of the composite were improved.

Influence of Weave Structures on the Tribological Properties of Hybrid Kevlar/PTFE Fabric Composites

The existing research of the woven fabric self-lubricating liner mainly focus on the tribological performance improvements and the service life raised by changing different fiber type combinations, adding additive modification, and performing fiber surface modification. As fabric composites, the weave structures play an important role in the mechanical and tribological performances of the liners. However, hardly any literature is available on the friction and wear behavior of such composites with different weave structures. In this paper, three weave structures （plain, twill 1/3 and satin 8/5） of hybrid Kevlar/PTFE fabric composites are selected and pin-on-flat linear reciprocating wear studies are done on a CETR tester under different pressures and different frequencies. The relationship between the tensile strength and the wear performance are studied. The morphologies of the worn surfaces under the typical test conditions are analyzed by means of scanning electron microscopy （SEM）. The analysis results show that at 10 MPa, satin 8/5 performs the best in friction-reduction and antiwear performance, and plain is the worst. At 30 MPa, however, the antiwear performance is reversed and satin 8/5 does not even complete the 2 h wear test at 16 Hz. There is no clear evidence proving that the tensile strength has an influence on the wear performance. So the different tribological performance of the three weave structures of fabric composites may be attributed to the different PTFE proportions in the fabric surface and the different wear mechanisms. The fabric composites are divided into three regions： the lubrication region, the reinforced region and the bonding region. The major mechanisms are fatigue wear and the shear effects of the friction force in the lubrication region. In the reinforced region fiber-matrix de-bonding and fiber breakage are involved. The proposed research proposes a regional wear model and further indicates the wear process and the wear mechanism of fabric composites.

Tribological Properties and Failure Analysis of PTFE Composites used for Seals in the Transmission Unit

The sealing rings are one of the most important components as the sealing devices in the wet clutch unit of a heavy vehicle. The sealing ring, made from PTFE composites, was subjected to serious wear on the sealing surface, but the mating metal surface only had slight abrasion. A specialized test rig was designed for wear research and failure analysis of the sealing ring. The composition analyses of the ring material, working conditions and wear surface characteristics by visual inspection and tribological properties as well as microscopic analysis with scanning electron microscope was performed to determine the wear mechanism and failure causes. Results revealed that the wear of PTFE composites was characterized by abrasion and adhesion after a certain duration testing, and the wear mechanism changed to thermal fatigue and abrasive wear in the stage of intense wear. The thermal deformation and fatigue were primarily responsible for the rapid wear of the PTFE composites for the sealing rings.

In situ formation of Zr_2Al_3C_4/Al_2O_3 composites by combustion synthesis with PTFE and thermal activations

Preparation of Zr2Al3C4-Al2O3 in situ composites was investigated by self-propagating high-temperature synthesis(SHS)involving both aluminothermic reduction of ZrO2 and chemical activation of PTFE(Teflon).The starting materials included ZrO2,Al,carbon black and PTFE.In addition to the conventional SHS method,the experiments were conducted by a chemical-oven SHS(COSHS)route to thermally assist the synthesis reaction.The threshold amount of 2%(mass fraction)PTFE was required to induce self-sustaining combustion.When the conventional SHS scheme was utilized,due to low combustion temperatures between 1152 and 1272°C and insufficient reaction time,the dominant carbide forming in the composite was ZrC instead of Zr2Al3C4.On the other hand,the COSHS technique increased the combustion temperature of the reactant compact to about 1576°C,lengthened the high-temperature duration for the reaction,and prevented Al vapor from escaping away.As a consequence,Zr2Al3C4-Al2O3 composites with a small amount of Zr3Al3C5 were obtained.The microstructure of the COSHS-derived product showed that plate-like Zr2Al3C4 grains were about 2μm in thickness and 10-30μm in length,and most of them were closely stacked into a laminated configuration.

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.

Effect of heat treatment on microstructure and thermophysical properties of diamond/2024 Al composites

50%diamond particle （5μm） reinforced 2024 aluminum matrix （diamond/2024 Al） composites were prepared by pressure infiltration method. Diamond particles were distributed uniformly without any particle clustering, and no apparent porosities or significant casting defects were observed in the composites. The diamond-Al interfaces of as-cast and annealed diamond/2024 Al composites were clean, smooth and free from interfacial reaction product. However, a large number of Al2Cu precipitates were found at diamond-Al interface after aging treatment. Moreover, needle-shaped Al2MgCu precipitates in Al matrix were observed after aging treatment. The coefficient of thermal expansion （CTE） of diamond/2024 Al composites was about 8.5×10-6 °C-1 between 20 and 100 °C, which was compatible with that with chip materials. Annealing treatment showed little effect on thermal expansion behavior, and aging treatment could further decrease the CTE of the composites. The thermal conductivity of obtained diamond/2024 Al composites was about 100 W/（m？K）, and it was slightly increased after annealing while decreased after aging treatment.

Microstructure and thermophysical properties of SiC/Al composites mixed with diamond

The thermophysical properties of the SiC /Al composites mixed with diamond（SiC-Dia/Al） were studied through theoretical calculation and experiments. The thermal conductivity and the thermal expansion coefficient of the SiC-Dia/Al were calculated by differential effective medium（DEM） theoretical model and extended Turner model, respectively. The microstructure of the SiC-Dia/Al shows that the combination between SiC particles and Al is close, while that between diamond particles and Al is not close. The experimental results of the thermophysical properties of the SiC-Dia/Al are consistent with the calculated ones. The calculation results show that when the volume ratio of the diamond particles to the SiC particles is 3：7, the thermal conductivity and the thermal expansion coefficient can be improved by 39% and 30% compared to SiC/Al composites, respectively. In other words, by adding a small amount of diamond particles, the thermophysical properties of the composites can be improved effectively, while the cost increases little.

WC-Ni_3Al-B composites prepared through Ni+Al elemental powder route

In order to develop the liquid phase sintering process of WC-Ni3Al-B composites,the preparation process of WC＋Ni3Al prealloyed powder by reaction synthesis of carbonyl Ni,analytical purity Al and coarse WC powders was investigated.DSC and XRD were adopted to study the procedure of phase transformation for the 3Ni＋Al and 70%WC＋（3Ni＋Al） mixed powders in temperature ranges of 550-1200 °C and 25-1400 °C,respectively.The results demonstrate that the formation mechanism of Ni3Al depends on the reaction temperature.Besides WC phase,there exist Ni2Al3,NiAl and Ni3Al intermetallics in the powder mixture after heat treatment at 200-660 °C,while only NiAl and Ni3Al exist at 660-1100 °C.Homogeneous WC＋Ni3Al powder mixture can be obtained in the temperature range of 1100-1200 °C.The WC-30%（Ni3Al-B） composites prepared from the mixed powders by conventional powder metallurgy technology show nearly full density and the shape of WC is round.WC-30%（Ni3Al-B） composites exhibit higher hardness of 9.7 GPa,inferior bending strength of 1800 MPa and similar fracture toughness of 18 MPa-m1/2 compared with commercial cemented carbides YGR45（WC-30%（Co-Ni-Cr））.

Microstructure and properties of Al/Si/SiC composites for electronic packaging

The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration.On the premise of keeping the machinability of the composites,the silicon carbide particles,which have the similar size with silicon particles（average 13 μm）,were added to replace silicon particles of same volume fraction,and microstructure and properties of the composites were investigated.The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites.It is also observed that higher thermal conductivity（TC） and flexural strength will be obtained with the addition of SiC particles.Meanwhile,coefficient of thermal expansion（CTE） changes smaller than TC.Models for predicting thermal properties were also discussed.Equivalent effective conductivity（EEC） was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.

Morphology and Frictional Characteristics Under Electrical Currents of Al_2O_3/Cu Composites Prepared by Internal Oxidation

Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.

Microstructures,mechanical and oxidation behaviors of C/C composites modified by NiAl alloy

Carbon/carbon composites modified by NiAl alloy were prepared using vacuum reactive melt infiltration methods with NiAl and titanium mixed powders as raw materials. The microstructures were investigated by scanning electron microscopy. The fracture behavior, infiltration and oxidation mechanism were further discussed. The results indicated that NiAl alloy exhibited good wettability on the C/C preform because a TiC reaction layer formed at the interface. Multi-layer（PyC/TiC/NiAl＋TiC） coating evenly and compactly distributed on the surface of the carbon fiber in tubular form. The penetration depth of molten NiAl alloys depended on the reaction between the PyC and titanium. The impact fracture was inclined to along the interface between the NiAl permeability layer and C/C matrix. Al_2TiO_5 and TiO_2 formed on the surface, while the interior multi-layer tubular structure partially remained after oxidation at 1773 K for 30 min.

Development of Al-12Si-xTi system active ternary filler metals for Al metal matrix composites

To improve the wettability of Al metal matrix composites（Al-MMCs） by common filler metals,Al-12Si-xTi（x=0.1,0.5,1,3.0;mass fraction,%） system active ternary filler metals were prepared.It was demonstrated that although the added Ti existed within Ti（Al1-xSix）3（0≤x≤0.15） phase,the shear strength and shear fracture surface of the developed Al-12Si-xTi brazes were quite similar to those of traditional Al-12Si braze due to the presence of similar microstructure of Al-Si eutectic microstructure with large volume fraction.So,small Ti addition（～1%） did not make the active brazes brittle and hard compared with the conventional Al-12Si braze.The measured melting range of each Al-12Si-xTi foil was very similar,i.e.,580-590 ℃,because the composition was close to that of eutectic.For wettability improvement,with increasing Ti content,the interfacial gap between the Al2O3 reinforcement and filler metal（R/M） could be eliminated,and the amount of the remainder of the active fillers on the composite substrate decreased after sessile drop test at 610 ℃ for 30 min.So,the wettability improvement became easy to observe repeatedly with increasing Ti content.Additionally,the amount and size of Ti（AlSi）3 phase were sensitive to the Ti content（before brazing） and Si content（after brazing）.

Hot deformation and processing maps of Al_2O_3/Al composites fabricated by flake powder metallurgy

The deformation behaviors of Al2O3/Al composites were investigated by compressive tests conducted at temperature of 300-450 °C and strain rates of 0.001-1.0 s-1 with Gleeble-1500 D thermal simulator system. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The hyperbolic sine constitutive equation can describe the flow stress behavior of Al2O3/Al composites, and the deformation activation energy and constitutive equations were calculated. The processing maps of Al2O3/Al-2 μm and Al2O3/Al-1 μm composites at strain of 0.6 were obtained and the optimum processing domains are in ranges of 300-330 °C, 0.007-0.03 s-1 and 335-360 °C, 0.015-0.06 s-1 for hot working, respectively. The instability zones of flow behavior can also be recognized by the maps.

Microstructure and evolution of(TiB_2+Al_2O_3)/NiAl composites prepared by self-propagation high-temperature synthesis

（TiB2＋Al2O3）/NiAl composites were synthesized by self-propagation high-temperature synthesis, and their phase compositions, microstructures and evolution modes were studied. The microstructures and shapes vary with the TiB2＋Al2O3 content in the NiAl matrix. TiB2 particles take a great variety of elementary shapes such as white bars, plates, herringbones, regular cubes and cuboids. These results outline a strategy of self-assembly processes in real time to build diversified microstructures. Some TiB2 grains in sizes of 2-5μm are embeded in Al2O3 clusters, while a small number of TiB2 particles disperse in the NiAl matrix. It is believed that the higher the TiB2＋Al2O3 content is, the more the regular shapes and homogeneous distributions of TiB2 and Al2O3 will be present in the NiAl matrix.

Effect of CuO particle size on synthesis temperature and microstructure of Al_2O_(3p)-Al composites from Al-CuO system

Al2O3p-Al composites were synthesized using an in-situ reaction in the 80%Al-20%CuO （mass fraction） system. The effects of the CuO particle size on the synthesis temperature and microstructure of the composites were investigated by various methods. The results indicate that the CuO particle size has a significant effect on the temperature at which the complete reaction in the Al-CuO system occurs：the temperature is 200 ℃ lower in the Al-CuO system containing CuO particles with sizes less than 6μm than that containing CuO particles with sizes less than 100μm. The interfacial bonding between Al2O3 particles and Al is not complete when the temperature is below a critical value. The morphology of the Al2O3 particles varies from ribbon-like shape to near spherical shape when the temperature is above a critical value. These two critical temperatures are affected by the particle size of CuO, and the critical temperature of the sample containing CuO particles with sizes less than 6μm is 100 ℃ lower than that of the sample containing CuO particles with sizes less than 100μm.

Experimental study and numerical analysis on dry friction and wear performance of co-continuous SiC/Fe-40Cr against SiC/2618 Al alloy composites

The dry friction and wear behaviors of co-continuous composites SiC/Fe–40Cr against SiC/Al 2618 alloy were investigated on a ring-on-ring friction and wear tester at sliding speed of 30-105 m/s under the load of 1.0-2.5 MPa. The experimental result reveals that the characteristic of two body abrasive wear and oxidation wear mechanisms are present for SiCn/2618 Al composite under higher load and sliding speed. SiC ceramic continuous network as the reinforcement can avoid composite from the third body wear that usually occurs in traditional particle reinforced composite. The mechanically mixed layer (MML) controls greatly the wear rate and friction coefficient of the composites. The composites tested at higher sliding speed exhibit higher value of friction coefficient and fluctuation, which is associated with the intermittent formation and removal of the MML. The wear and stress—strain behaviors of SiCn/Fe–40Cr against SiCn/Al 2168 at 30-105 m/s under 1.0-2.5 MPa were analyzed by finite element method with the software Solidwork2012 Simulation, respectively. The wear and stress–strain behavior of the composite predicted by the FEM correlated well with the experimental results.