Centrifugal casting of a reinforced hypereutectic silumin

Centrifugal casting is used to form composite materials with a gradient structure. Hardening particles are shown to affect the hardness of the composite materials.     

镁对过共晶铝铁合金组织形貌的影响

针对普通熔铸条件下过共晶Al-Fe合金初生富铁相严重割裂基体、恶化合金性能的问题,采用元素Mg对过共晶Al-5%Fe合金进行变质细化处理,Mg以Al-10%Mg中间合金形式加入。借助光学显微镜等分析了Al-10%Mg中间合金晶粒细化剂加入量和熔体保温时间对过共晶Al-5%Fe合金微观组织形貌及性能的影响。试验表明:在过共晶Al-5%Fe合金中加入Al-10%Mg中间合金细化剂,当加入量为1.2%、保温时间90min时,细化效果较好,Al-5%Fe合金中初生A13Fe相由未添加细化剂时的粗大板条状变为花朵状和颗粒状,并且尺寸明显减小,从而显著提高材料的强度和塑性。     

On solidification of hypereutectic Al-Si alloys

Precipitation of primary silicon was studied in Al-Si hypereutectic alloys with 15, 18, and 25 wt. % silicon content. The alloys were solidified with different cooling rates from different super heat temperatures. The liquidus and eutectic temperature were evaluated from the cooling curves. The liquidus temperature was found to decrease with cooling rate. The evaluation of microstructure showed that the fraction of primary silicon decreased with increasing the cooling rate and super heat temperature. Furthermore, the morphology of the primary silicon changed as an effect of cooling rate and super heat temperature.     

Effect of plastic deformation on the mechanical properties and the fine-structure parameters of Pb-Ca-Sn alloys

The specific features of structure formation in Pb-Ca-Sn alloys intended for battery current leads are considered. The effect of plastic deformation on the mechanical properties and the fine-structure parameters in Pb-0.1% Ca-0.3% Sn and Pb-0.05% Ca-1.1% Sn alloys is studied. The influence of the initial structure on the mechanical properties and the fine-structure parameters of the alloys is shown, and the variation of the alloy properties under plastic deformation is demonstrated.     

Effect of geometrical structural parameters on the strength properties of hard alloys based on titanium carbide

Experimental data on the strength properties of titanium carbide hard alloys prepared under different sintering conditions were obtained. The relationship of properties to the geometrical structural parameters is elucidated. It was established that the transverse bend strength increases with decrease in the degree of contact of the carbide grains.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 82–85, March–April, 1995.     

Semi-solid rapid compression testing of spray-formed hypereutectic Al-Si alloys

The rheology of Al-30Si-5Cu and Al-30Si-5Cu-2Mg spray-formed alloys has been characterized after holding at various times and temperatures, using semisolid rapid compression to obtain load-displacement curves. Microstructures were examined after partial remelting and compression in an attempt to understand the flow behavior. The initial resistance to flow generally increased with holding time at temperature. This increase was attributed to the increased strength of a three-dimensional (3-D) solid silicon network present in these alloys in the semisolid state, with the initial resistance to flow smaller in the magnesium-containing alloys. With increased temperature, the initial resistance decreased due to increased liquid content and grain spheroidization. The viscosity vs shear rate response was studied using the approach of Laxmanan and Flemings. The materials shear thinned rapidly during the test conditions, in which the shear rate rapidly increased from approximately 2.5 to 92 s⁻¹. The results were fitted to a power-law model, and the viscosities showed a drop of approximately two to four orders of magnitude when extrapolated to a shear rate of 1000 s⁻¹ (a typical value in actual component manufacture). The rapid compression test, which is close to conditions present in component manufacture, was shown to have more in common with a shear rate jump experiment, rather than steady-state viscometry.     

Effect of sliding and rolling friction on the energy-force parameters during hot rolling in four-high stands

A procedure for the calculation of the main-drive power for a hot-rolling wide-strip mill is developed. It takes into account that 85–99% of the lengths of the deformation zones in the working stands of such mills are occupied by stick zones, in which a strip undergoes static friction stresses (which do useful work only in the backward slip zone). This procedure also takes into account the rolling friction energy losses, which account for 83–93% of the power consumed for the rotation of idle backup rolls or 29–68% of the total energy consumed by the main mill drive. The average power calculation error for this procedure is 5%, and the maximum error is 10%, which is three to five times smaller than the errors of well-known calculation procedures. Our procedure has a high potential for revealing the reserves of decreasing the contact stresses in rolls and the saving of electric power via the redistribution of the reductions and tensions between stands and an increase in the temperature of the semi-finished rolled products.     

脉冲电流参数对过共晶高铬铸铁近液相线熔化后凝固组织的影响

对过共晶高铬铸铁近液相线溶化后的凝固过程进行脉冲电流处理,研究了脉冲电流参数（脉冲电压和频率）对凝固组织的影响.发现脉冲频率和电压的增大都有助于过共晶高铬铸铁凝固组织中碳化物的细化和粒化.脉冲频率的增大促进大量细小颗粒状初生碳化物的析出,离异共晶现象变得更加明显,层片状共晶碳化物减少.脉冲电压的增加促进初生碳化物细化和粒化,片状共晶碳化物变短.过高的电压也促进离异共晶,导致更多的初生碳化物的形成.     

Trace element effects on ductility and fracture of Ni-Cr-Ce alloys

The effect of trace additions of Ce, ranging from Oto 180 at. ppm, on the tensile behavior of a Ni-20Cr alloy is presented. For alloys without Ce a transition from ductile transgranular to brittle intergranular fracture mode is observed at high temperatures and for low strain-rate tests. Additions of Ce suppress this transition with a resulting increase in ductility. Maximum effects are observed for temperature and strain rate values where fracture in Ce-free alloys occursvia grain boundary cavitation. The reduced cavitation rate of Ce-containing alloys is suggested to be the result of an increase in both interfacial energy and grain boundary mobility. Formerly Graduate Assistant, Department of Mechanics and Materials Science, Rutgers     

Tensile ductility of superplastic ceramics and metallic alloys

Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-rate-sensitivity exponent, m, is high (m⩾0.5). The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminium, nickel and titanium alloys) is primarily a function of the strain-rate-sensitivity exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia-alumina composites and iron carbide) is not only a function of the strain-rate-sensitivity exponent, but also a function of the parameter ⋗e exp (Q_c/RT) where ⋗e is the steady-state strain rate and Q_c is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase in ⋗e exp (Q_c/RT). This trend in tensile elongation is explained based on a “fracture-mechanics” model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase in the parameter (2γ_s−γ_gb), where γ_s is the surface energy and γ_gb is the grain boundary energy. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.     

Effect of neodymium on primary silicon and mechanical properties of hypereutectic Al-15%Si alloy

The mechanical properties of hypereutectic Al-Si alloys are mainly determined by size and morphology of the primary silicon phase.So,optical microscopy(OM) and X-ray diffraction(XRD) were adopted to study affection of Nd on primary silicon of hypereutectic Al-15%Si alloy in this paper.The results of OM showed that pure Nd could effectively refine primary silicon of hypereutectic Al-15%Si alloy.When Nd addition was 0.3%,the average size of primary silicon reduced from 20-40 μm of initial sample to 10-20 μm of modified sample.XRD pattern showed that no new phase was formed after Nd modification.The results of mechanical properties test showed that whole properties of modified samples were significantly improved.Tensile strength increased about 32.6% from 147 MPa to 195 MPa.Elongation was increased about 160% from 1.0% to 2.6%.The improvement of mechanical properties should attribute to primary silicon refinement after modification.     

Effect of alloying elements on the formation of rolling texture in Mg-Nd-Zr and Mg-Li alloys

The effect of alloying on the texture of Mg-Nd-Zr and Mg-Li alloy sheets is studied using pole and inverse pole figures. The basal texture intensity in rolling of Mg-Nd-Zr alloys is shown to be substantially decreased due to the precipitation of dispersed intermetallic Mg₁₂Nd phase particles. As a result, the workability characteristics during deep drawing can be increased. Lithium alloying causes the formation of a prismatic rolling texture, which is unusual for magnesium alloys, as a result of the phase transformation of the lithium-based bcc phase into the magnesium-based hexagonal close-packed phase that obeys the Burgers orientation relationships.     

Effect of process parameters on the microstructure and mechanical properties of vacuum hot-press sintered Co-50 mass% Cr alloys

In the present research, two different compositions of submicron-structured cobalt (800?±?45?nm) and chromium (700?±?50?nm) powders are mixed to fabricate Co-50 mass% Cr alloys by the vacuum hot-press sintering technique. This study imposes various hot-press sintering temperatures (1150, 1200, 1250 and 1300°C) and pressures (20, 30, 40 and 50?MPa) while maintaining the sintering time at 1?h, respectively. The experimental results show that the optimum parameters of hot-press sintered Co-50 mass% Cr alloys are 1200°C at 50?MPa for 1?h. Meanwhile, the sintered density reaches 7.73?g?cm^?3, the closed porosity decreases to 0.31%, and the hardness and transverse rupture strength values increase to 80.6?±?0.3 HRA and 1052.9?±?17.5?MPa, respectively. Grain growth is not obviously generated after 1200°C hot-press sintering at 50?MPa for 1?h. Consequently, the optimal solid-phase sintering process effectively improved hot-press sintered Co-50 mass% Cr alloys, which resulted in the good properties.