镁质料涂抹中间包技术的应用

济钢第一炼钢厂以涂抹料中间包替代绝热板中间包，经合理设计涂抹工艺及烘烤制度，中间包的平均寿命达到１９．９８炉。与使用绝热板中间包相比，平均连浇炉数由４７．６４炉提高到５１．１６炉，钢水收得率提高０．３５％，耐材消耗降低０．１５元／ｔ钢，并提高了钢水纯净度。

Microstructures and properties of Al-50%SiC composites for electronic packaging applications

Al？50%SiC （volume fraction） composites containing different sizesofSiC particles （average sizesof 23, 38 and 75 μm） were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the propertiesof the compositeswere investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion （CTE） and higher thermal conductivity （TC）, while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400℃for 6h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TCis improved. The TC, CTE and flexural strength of the Al/SiC composite with averageSiC particlesize of75 μm are 156 W/（m·K）, 11.6×10^-6K^-1 and 229 MPa, respectively.

Structural and mechanical properties of CuZr/AlN nanocomposites

Powder metallurgy method was used to prepare copper alloy nanocomposites （CuZr/AlN） with high strength and conductivity. Optical microscopy, high-resolution transmission electron microscopy and other methods were adopted to study the impact of different sintering technologies on the structural and mechanical properties as well as the impact of solution and aging treatments on the mechanical properties of CuZr/AlN. The result shows that the specimen has a dense structure, and the size of the crystal grain is around 0.2 μm. The Brinell hardness of the specimen increases with the increase in re-pressing pressure and sintering temperature. The Brinell hardness of specimen also increases with the increase in zirconium content. However, above 0.5%（mass fraction） of zirconium content, the Brinell hardness of the nanocomposites is reduced. The buckling strength of the specimens increases with the increase in re-pressing pressure and sintering temperature. The buckling strength is the highest when the zirconium content is 0.5%. The Brinell hardness is lower after solution and aging treatments at 900 ℃. The Brinell hardness of the CuZr/AlN series specimen after the aging treatment at 500 ℃ or 600 ℃ increases. The specimen was also over aged at 700 ℃.

Deformation behaviors and processing maps of CNTs/Al alloy composite fabricated by flake powder metallurgy

Deformation behaviors of CNTs/Al alloy composite fabricated by the method of flake powder metallurgy were investigated by hot compression tests, which were performed in the temperature range of 300?550 °C and strain rate range of 0.001? 10 s?1 with Gleeble?3500 thermal simulator system. Processing maps of the CNTs/Al alloy at different strains were calculated to study the optimum processing domain. Microstructures before and after hot compressions were characterized by electron backscattered diffraction (EBSD) method. Stress?strain curves indicate that the flow stress increases with the increase of strain rate and the decrease of temperature. The processing maps of the CNTs/Al alloy at different strains show that the optimum processing domain is 500?550 °C, 10 s?1 for hot working. EBSD analysis demonstrates that fully dynamic recrystallization occurs in the optimum processing domain (high strainrate 10 s?1), whereas the main soften mechanism is dynamic recovery at low strain rate (0.001 s?1).

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.

Effects of addition of NH_4HCO_3 on pore characteristics and compressive properties of porous Ti-10%Mg composites

Porous Ti-Mg composites were successfully fabricated through powder metallurgy processing with ammonium hydrogen carbonate （NH4HCO3） as a space-holder. The effects of NH4HCO3 on properties of porous composites were comprehensively investigated. The pore characteristics and compressive properties of the specimens were characterized by X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the porosity of the porous composites can be tailored effectively by changing the amount of NH4HCO3 added, and the use of NI-I4HCO3 has no influence on the microstructure and phase constituents of the Ti-10%Mg porous composites. The open porosity and compressive strength as well as compressive elastic modulus vary with the adding amount and particle size of NHaHCO3. When the mass fraction of NHaHCO3 added is 25%, elastic modulus and compressive strength of composites with porosity of around 50% are found to be similar to those of human bone.

Effect of glass fibre(GF) addition on microstructure and tensile property of GF/Pb composites fabricated by powder metallurgy

GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that relative densities decrease with increasing GF fraction, and the 50μm-GF reinforced specimens exhibit a better densification than the 300μm-GF reinforced ones. The GF particles distribute quite uniformly inPb matrix, and the composites fabricated at low sintering temperature （〈200℃） possess fine-grain microstructure. The addition of GF significantly improves the strength of the Pb composites, and the ultimate tensile strength of the Pb composite reinforcedwith the addition of 50μm-0.5% GF（mass fraction）is about 30MPa higher than that of GF-free sample. For all composites groups, increasing the reinforcement content from 0.5%to 2%（mass fraction）results in a decrease in both tensile strength and ductility.

Production of Ag-ZnO powders by hot mechanochemical processing

Ag–CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties.Nevertheless,considering the restriction on using Cd due to its toxicity,it is necessary to find alternative materials that can replace these composites.In this study,the synthesis of Ag-ZnO alloys from Ag-Zn solid solutions was investigated by hot mechanochemical processing.The hot mechanochemical processing was conducted in a modified attritor mill at 138℃under flowing O2 at 1200 cm3/min for 3.0 h.The microstructure and phase evolution were investigated using X-ray diffractometry,field emission gun scanning electron microscopy and transmission electron microscopy.The results suggest that it is possible to complete the oxidation of Ag-Zn solid solution by hot mechanochemical processing at a low temperature and short time.This novel synthesis route can produce Ag-ZnO composites with a homogeneous distribution of nanoscale ZnO precipitates,which is impossible to achieve using the conventional material processing methods.Considering the fact that the fundamental approach to improving electric contact material performance resides in obtaining uniform dispersion of the second-phase in the Ag matrix,this new processing route could open the possibility for Ag-ZnO composites to replace non-environmentally friendly Ag-CdO.

Friction behavior of Ti-30Fe composites strengthened by TiC particles

Ti-Fe-x TiC(x=0, 3, 6, 9, wt.%) composites were fabricated through low temperature ball milling of Ti, Fe and TiC powders, followed by spark plasma sintering. The results show that β-Ti, β-Ti-Fe, η-Ti4 Fe2 O0.4 and TiC particles can be found in the composites. The microstructure can be obviously refined with increasing the content of TiC particles. The coefficient of friction(COF) decreases and the hardness increases with increasing the content of TiC particles. The adhesive wear is the dominant wear mechanism of all the Ti-Fe-x TiC composites. The Ti-Fe-6 TiC composite shows the best wear resistance, owing to the small size and high content of TiC particle as well as relatively fine microstructure. The wear rate of the Ti-Fe-6 TiC composite is as low as 1.869× 10-5 mm3/(N·m) and the COF is only 0.64. Therefore, TiC particle reinforced Ti-Fe based composites may be utilized as potential wear resistant materials.

Effect of iron addition on microstructure, mechanical and magnetic properties of Al-matrix composite produced by powder metallurgy route

The effect of iron addition on the microstructure, mechanical and magnetic properties of Al-matrix composite was studied. Mechanical mixing was used for the preparation of 0, 5%, 10% and 15% Fe-Al composites（mass fraction）. Mixtures of Al-Fe were compacted and sintered in a vacuum furnace at 600 °C for 1 h. X-ray diffraction（XRD） of the samples containing 5% and 10% Fe indicates the presence of Al and Fe peaks, while sample containing 15% Fe reveals Al and Al13Fe4 peaks. The results show that both densification and thermal conductivity of the composites decrease by increasing the iron content. The presence of iron in the composite improves the compressive strength and the hardness. The strengthening mechanism is associated with the grain refinement of the matrix and uniform distribution of the Fe particles, as well as the formation of Al13Fe4 intermetallic. The measured magnetization values are equal to 0.3816×10-3 A·m2/g for 5% Fe sample and increases up to 0.6597×10-3 A·m2/g for 10% Fe sample, then decreases to 0.0702×10-3 A·m2/g for 15% Fe sample. This can be explained by the formation of the diamagnetic Al13Fe4 intermetallic compound in the higher Fe content sample detected by XRD analysis.

Microstructure and dry sliding wear behavior of Cu-Sn alloy reinforced with multiwalled carbon nanotubes

Multiwalled carbon nanotubes （MWCNTs） reinforced Cu-Sn alloy based nanocomposite was developed by powder metallurgy route. The mass fraction of CNTs was varied from 0 to 2% in a step of 0.5%. The developed nanocomposites were subjected to density, hardness, electrical conductivity, and friction and wear tests. The results reveal that the density of nanocomposite decreases with the increase of the mass fraction of CNTs. A significant improvement in the hardness is noticed in the nanocomposite with the addition of CNTs. The developed nanocomposites show low coefficient of friction and improved wear resistance when compared with unreinforced alloy. At an applied load of 5 N, the coefficient of friction and wear loss of 2%CNTs reinforced Cu-Sn alloy nanocomposite decrease by 72% and 68%, respectively, compared with those of Cu-Sn alloy. The wear mechanisms of worn surfaces of the composites are reported. In addition, the electrical conductivity reduces with the increase of the content of CNTs.

Microstructure,mechanical and wear properties of aluminum borate whisker reinforced aluminum matrix composites

The microstructural features and the consequent mechanical properties were characterized in aluminium borate whisker(ABOw)(5, 10 and 15 wt.%) reinforced commercially-pure aluminium composites fabricated by conventional powder metallurgy technique. The aluminium powder and the whisker were effectively blended by a semi-powder metallurgy method. The blended powder mixtures were cold compacted and sintered at 600 ℃. The sintered composites were characterized for microstructural features by optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), transmission electron microscopy(TEM) and X-ray diffraction(XRD) analysis. Porosity in the composites with variation in ABOw contents was determined. The effect of variation in content of ABOw on mechanical properties, viz. hardness, bending strength and compressive strength of the composites was evaluated. The dry sliding wear behaviour was evaluated at varying sliding distance at constant loads. Maximum flexural strength of 172 MPa and compressive strength of 324 MPa with improved hardness around HV 40.2 are obtained in composite with 10 wt.% ABOw. Further increase in ABOw content deteriorates the properties. A substantial increase in wear resistance is also observed with 10 wt.% ABOw. The excellent combination of mechanical properties of Al-10 wt.%ABOw composites is attributed to good interfacial bonds, less porosity and uniformity in the microstructure.

Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl2O3 nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process.The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured.It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders.The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al2O3 content of 10 wt.%.Mechanical properties were controlled by Al2O3 content,dispersion of nano reinforcements and grain size.The optimum hardness and strength properties were achieved through incorporation of 10 wt.%Al2O3 and homogenous dispersion of CNTs and Al2O3 nanoparticles(NPs)at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement.Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al2O3 content and milling time.The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al2O3 and also less inter-particle spacing in the matrix.The larger Al2O3 content and more homogenous dispersion of CNTs and Al2O3 NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.

Combined powder metallurgy routes to improve thermal and mechanical response of Al−Sn composite phase change materials

Powder metallurgy processes are suitable to produce form-stable solid−liquid phase change materials from miscibility gap alloys.They allow to obtain a composite metallic material with good dispersion of low-melting active phase particles in a high-melting passive matrix,preventing leakage of the particles during phase transition and,therefore,increasing the stability of thermal response.Also,the matrix provides structural properties.The aim of this work is to combine conventional powder mixing techniques(simple mixing and ball milling)to improve active phase isolation and mechanical properties of an Al−Sn alloy.As matter of fact,ball milling of Sn powder allows to reduce hardness difference with Al powder;moreover,ball milling of the two powders together results in fine microstructure with improved mechanical properties.In addition,different routes applied showed that thermal response depends on the microstructure and,in particular,on the particle size of the active phase.In more detail,coarse active phase particles provide a fast heat release with small undercooling,while small particles solidify more slowly in a wide range of temperature.On the other hand,melting and,consequently,heat storage are independent of the particle size of the active phase.This potentially allows to“tailor”the thermal response by producing alloys with suitable microstructure.

Effect of Ti−6Al−4V particle reinforcements on mechanical properties of Mg−9Al−1Zn alloy

Mg−9Al−1Zn(AZ91)magnesium matrix composites reinforced by Ti−6Al−4V(TC4)particles were successfully prepared via powder metallurgical method.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)showed a mountain-like tendency with the increase of the TC4 content.The mechanical properties of AZ91 magnesium matrix composites reached the optimal point with TC4 content of 10 wt.%,realizing YS,UTS,and EL of 335 MPa,370 MPa,and 6.4%,respectively.The improvement of mechanical properties can be attributed to the effective load transfer from the magnesium matrix to the TC4 particles,dislocations associated with the difference in the coefficient of thermal expansion,good interfacial bonding between the Mg matrix and TC4 particles,and grain refinement strengthening.

Densification process of 10%B_4C-AA2024 matrix composite strips by semi-solid powder rolling

Semi-solid powder rolling（SSPR） is a novel strip manufacturing process,which includes the features of semi-solid rolling and powder rolling.In this work,densification process and deformation mechanisms of B4 C and AA2024 mixed powders in the presence of liquid phase were investigated.The relationships between relative densities and rolling forces were analyzed as well.The results show that liquid fraction plays an important role in the densification process which can be divided into three stages.Rolling deformation is the main densification mechanism in deformation area when the liquid fraction is lower than 20%.When the liquid fraction is equal to or higher than 20%,the flowing and filling of liquid phase are the densification mechanisms in deformation area.The relative densities increase with increasing rolling forces.The relative density–rolling force curves are similar at 550 °C and 585 °C.The characteristics of the curve shapes are apparently different at 605 °C and 625 °C.

Damping capacity of high strength-damping aluminum alloys prepared by rapid solidification and powder metallurgy process

Two kinds of high strength-damping aluminum alloys （LZ7） were fabricated by rapid solidification and powder metallurgy （RS-PM） process. One material was extruded to profile aluminum directly and the other was extruded to bar and then rolled to sheet. The damping capacity over a temperature range of 25-300 ℃was studied with damping mechanical thermal analyzer （DMTA） and the microstructures were investigated by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that the damping capacity increases with the test temperature elevating. Internal friction value of rolled sheet aluminum is up to 11.5×10^-2 and that of profile aluminum is as high as 6.0×10^-2 and 7.5×10^-2 at 300 ℃, respectively. Microstructure analysis shows the shape of precipitation phase of rolled alloy is more regular and the distribution is more homogeneous than that of profile alloy. Meanwhile, the interface between particulate and matrix of rolled sheet alloy is looser than that of profile alloy. Maybe the differences at interface can explain why damping capacity of rolled sheet alloy is higher than that of profile alloys at high temperature （above 120 ℃）.

Influence of rutile(TiO_2) content on wear and microhardness characteristics of aluminium-based hybrid composites synthesized by powder metallurgy

The effect of rutile（TiO_2） content on the wear and microhardness properties of aluminium（Al）-based hybrid composites was explored. The proposed content of TiO_2（0, 4%, 8%, 12%, mass fraction） was blended to Al-15% SiC composites through powder metallurgy（P/M） process. Wear test was conducted using pin-on-disc apparatus under dry sliding conditions. Fabricated preforms were characterized using X-ray diffractometer（XRD）, scanning electron microscope（SEM） and energy-dispersive X-ray spectrometer（EDS）. Optical micrographs of the composite preforms display uniform distribution of TiO_2 throughout the matrix. Quantitative results indicate that wear resistance and microhardness increase with the increase of TiO_2 content. SEM images unveil that high wear resistance is attributed to high dislocation density of deformed planes and high hardness of TiO_2. SEM images of wear debris display gradual reduction in mean size of debris when TiO_2 content increases. EDS spectra confirm the presence of oxide layer which obviously reduces the effective area of contact between the sliding surfaces thereby lowers the wear loss of composites. The observation concludes that delamination and adhesive wear are the predominant mechanisms.

Prediction of Final Velocity of Aramid Fabric-Resin Composite Laminates Subjected to Ballistic Impact

The strain rate effects of aramid fiber material, quasi-static and ballistic impact perforation of composite laminates made of aramid fabric and phenolic resin/PVB are investigated respectively by means of MTS, split Hopkinson tension bars and ballistic impact apparatus. The tensile impact experiments on aramid fiber material are performed in strain rate range from 0.01/s to 1000/s. Experimental results show that the mechanical properties of aramid fiber material are insensitive to strain rate in the range from 0. 01/s to 1 000/s. An energy model to predict final velocity of composite laminates subjected to ballistic impact is proposed on the basis of experimental data of quasi-static perforation through the targets. The predicted final velocities show good agreement with the experimental final velocity.

Fabrication of Mg(OH)_2 Powders by Decomposition of Mg_3N_2 Powders

Mg（OH）2 powders were formed by the decomposition of Mg3N2 powders synthesized by a simple reaction of Mg with N Ha. X-ray diffraction（XRD）, Fourier transform infrared spectroscopy （FTIR）, and scanning electron microscopy（SEM） were used to study the structure, composition and morphology of the products. Mg （OH）2 nanowires with an average diameter about 300 nm-500 nm were found in these Mg（OH）2 powders.