Interfacial microstructure and properties of diamond/Cu-xCr composites for electronic packaging applications

Diamond/Cu-xCr composites were fabricated by pressure infiltration process.The thermal conductivities of diamond/Cu-xCr（x = 0.1,0.5,0.8） composites were above 650 W/mK,higher than that of diamond/Cu composites.The tensile strengths ranged from 186 to 225 MPa,and the bonding strengths ranged from 400 to 525 MPa.Influences of Cr element on the thermo-physical properties and interface structures were analyzed.The intermediate layer was confirmed as Cr3C2 and the amount of Cr3C2 increased with the increase of Cr concentration in Cu-xCr alloys.When the Cr concentration was up to 0.5 wt.%,the content of the Cr3C2 layer was constant.As the thickness of the Cr3C2 layer became larger,the composites showed a lower thermal conductivity but higher mechanical properties.The coefficients of thermal expansion（CTE） of diamond/Cu-xCr（x = 0.1,0.5,0.8） composites were in good agreement with the predictions of the Kerner＇ model.

Microstructure and formation mechanism of titanium matrix composites coating on Ti-6Al-4V by laser cladding

Laser cladding experiments were done on a 5-kW continuous wave CO2 laser to synthesize TiC and TiB rein- fowed titanium matrix composite coatings on Ti-6AI-4V alloy with a mixture of Ti and B4C precursor powder. The ther- modynamics of the reactions were calculated and analyzed. The microstructure and phase evolution of TiB and TiC com- posites were investigated. The results showed that the chemical reaction between Ti and B4C would release much heat, and these compounds, TiC, TiB, and small amount of TiB2, can be formed on the surface of Ti-6AI-4V alloy if the supplied en- ergy is sufficient to excite the reaction among the initial products. A good metallurgical bond between the coating and the substrate can be achieved. The microhardness of coating was irregular and the maximum value was approximately HV600.

Research on development of in situ titanium matrix composites and in situ reaction thermodynamics of the reaction systems

The in situ synthesis method for titanium matrix composites （TMCs） has obvious technical and economical advantages over other traditional methods. Ultrafine reinforcement particles were formed in situ by chemical reaction between elements or between elements and compounds. Using the approach, contamination at the composite matrix/reinforcement particle interface did not occur, interface bonding was good, and the reinforcement particle was thermodynamically stable. The stage of development of the preparation process for in situ TMCs as well as the thermodynamic analysis of the possible in situ reaction systems was described.

Effect of additional elements on aging behavior of Al-Zn-Mg-Cu alloys by spray forming

The microstructure and aging behavior of spray formed Al-Zn-Mg-Cu alloys were investigated as a function of alloying element addition. It is revealed that the grains of the as-deposited alloys are refined with increasing Zn element, while the function of Ni addition is to reduce grain boundary particles and eutectic in the as-extruded condition. Particles containing Mg and Zn are found to increase with Zn content increasing, while the role of Ni is to reduce both the number and size of these particles. After uniform heat treatment, parts of educts in grain boundary have melted and the grains have not grown up obviously. After heat extrusion, the microstructure becomes denser and there are many precipitated phases in cross-section while there are second phase arranging along extruded direction in longitudinal section. During artificial aging, the increment of Zn content produces not much effect on peak hardness, in addition to an accelerated overage softening. An addition of about 0.13%Ni, however, gives rise to not only improved peak hardness but also an improvement of property stability at the ageing temperature.

Capillary wave formation on excited solder jet and fabrication of lead-free solder ball

A survey of solder ball production processes especially focusing on disturbed molten metal jet breakup process was made. Then the formation of capillary wave on tin melt jet in the way of rapid solidification was studied. A semi-empirical formula, which can be written as λ=C_ vib(σ/ρ) 1/3f -2/3 to predict the relationship between wavelength of capillary wave and frequency of imposed vibration was obtained. Sn-4.0Ag-0.5Cu lead free solder ball was successfully produced with tight distribution and good sphericity. The excited jet breakup process is promising for cost effectively producing solder ball.

Effects of Ho on the microstructure and mechanical properties of Mg-Zn-Ho-Zr magnesium alloys

The microstructure and mechanical properties of Mg-Zn-Ho-Zr alloys have been investigated in detail. The grain size of the as-cast Mg-Zn-Ho-Zr alloy was greatly decreased by the addition of Ho, and the grain growth during solution treatment was suppressed by Mg-Zn-Ho phases formed at grain boundaries. These thermally stable Mg-Zn-Ho phases could not completely dissolve into the matrix dur- ing solution treatment, and the strengthening effect of solution-plus-ageing treatment weakened. The addition of Ho can greatly enhance the high-temperature elongation of the Mg-Zn-Ho-Zr alloy, but the increase of high-temperature tensile strength was just a little.

Influence of extrusion temperature on microstructure and mechanical properties of Mg-4Y-4Sm-0.5Zr alloy

The solution-treated Mg-4Y-4Sm-0.5Zr alloy was extruded at temperatures from 325℃ to 500℃.Dynamic recrystallization(DRX) completely occurs when the alloy is extruded at 350℃and above.The grains of the extruded alloy are obviously refined by the occurrence of DRX.The average grain size of the extruded alloy increases with increasing the extrusion temperature,leading to a slight decrease of the ultimate tensile strength(UTS) and the yield strength(YS) .On the contrary,the UTS and YS of the extruded and aged alloy increase with increasing the extrusion temperature.Values of UTS of 400 MPa,YS larger than 300 MPa and elongation(EL) of 7%are achieved after extrusion at 400℃ and ageing at 200℃ for 16 h.Both grain refinement and precipitation are efficient strengthening mechanisms for the Mg-4Y-4Sm-0.5Zr alloy.

An analytical approach to modeling stress-strain relationship of particle-reinforced metal matrix composites

An analytical model was established to simulate the stress-strain curves of particle-reinforced metal matrix composites by the classical stress equilibrium equation and secant modulus method,where particle cracking and matrix tearing were taken into consideration.The stress-strain curves of the composites predicted by the model fit the experimental curves very well.The stressstrain relationship of the matrix affected by the particles is predicted exactly,and it is found that the yield stress of the matrix is influenced obviously by the particle content.The yield strength of the composites is also predicted by the model,and the results fit the experimental data very well.

Modification of Sn–1.0Ag–0.5Cu solder using nickel and boron

Effects of Ni and B additions on the microstructure and growth behavior of the intermetallic compound(IMC) of Sn–1.0Ag–0.5Cu alloys(SAC105) were investigated in this study. Results show that microadditions of Ni and B result in volume fraction of primary Sn increasing and the grain size decreasing observably. It is found that a large number of fine reinforcement particles with network-like shape are found in the solder, and the thickness of interfacial IMC layer in the solder joint is grew less than that of SAC105 with longer aging time. Shear test results reveal that as-soldered solder joints of microalloyed SAC105 have better shear strength than that of SAC105 solder alloy.

Evolution of thermo-physical properties of diamond/Cu composite materials under thermal shock load

In this paper, the two-flume method was used to study the change laws of the thermal conductivity and thermal expansion coefficient of diamond/Cu composite materials with 100, 300, and 500 cycle numbers, under the action of thermal shock load between-196 and 85 °C; the X-ray diffraction method（XRD） was used to study the change of the residual stress in the thermal shock process of the diamond/Cu composite materials; and the evolution of the fracture microstructure with different thermal shock cycle numbers was observed through scanning electron microscopy（SEM）. The results of the study show that the increase of the binder residue at the interface reduces the thermal shock stability of the diamond/Cu composite materials. In addition, under the thermal shock load between-196 and 85 °C, the residual stress of the diamond/Cu composite materials increases continuously with the increase of the cycle numbers, the increase of residual stress leads to a small amount of interface debonding, an increase of the interfacial thermal resistances, and a decrease of the constraints of low-expansion component on material deformation, thus the thermal conductivity decreases slightly and the thermal expansion coefficient increases slightly.