Advanced Materials Research Vols. 535-537

Abstract: The present paper deals with experimental studies on the long life fatigue behavior of GH4169 alloy. Using the ultrasonic fatigue testing technique, specimens of hourglass shape were fatigue tested in air at room temperature under fully reversed cyclic loading conditions (R=-1). The very high cycle fatigue property of GH4169 alloy was studied and the initiation mechanisms of fatigue cracks were investigated and analyzed with scanning electron microscopy (SEM) and energy dispersive atomic X-ray (EDX). Preliminary results indicate that the S-N curve displays a bilinear decreasing tendency within 10⁹ cycles and fatigue failure initiates from inclusions/defects on the specimen surface.

Abstract: In order to refine the microstructure of A356 alloy, the effect of different contents of Ti on A356 alloy was analyzed with scanning electron microscopy (SEM). Experimental results show that it is not following the law of the more the content of Ti is, the finer the microstructure in the range of 0% to 7.5% Ti. However, the microstructure undergoes a first refining as the content of Ti is less than 0.3% and then coarsening with the increasing of Ti. Further, the mechanism of grain refiner is explained from three aspects. Finally, the hardness of A356 alloy is studied to verify the effect of different contents of Ti. The results confirm that the variety of hardness is in accordance with that of microstructure.

Abstract: Semisolid A356 alloy was prepared by low superheat pouring and slightly electro- magnetic stirring(LSPSES). The fractal dimensions of primary phase morphology in semisolid A356 alloy were researched by the calculating program written to calculate the fractal dimensions of box-counting in the image of primary phase morphology in semisolid A356 alloy. The results indicated that the primary phase morphology in the alloy was characterized by fractal dimension, and the morphology obtained by the different processing parameters had the different fractal dimension. The morphology at the different position of ingot had the different fractal dimensions, which reflected the effect of solidified conditions at different position in the same ingot on the morphology in the alloy. Solidification of the alloy was a course of change in fractal dimension.

Abstract: In this paper, self-made tension machine was used to explore the evolution of recovery stress in cold drawing for NiTiNb alloy. The microstructure evolution in different cold drawing conditions was observed. The results show that due to the pre-strain temperature (213K) higher than Ms, the peak values of recovery stress are relatively poor (lower than 490MPa) after cold drawing. After hot drawing, the original spherical Nb particles were changed to thin piece of nano lines and the contribution of Nb nano lines (BCC structure) in NiTi matrix (B2) was greatly improved.

Abstract: Ti-6Al-7Nb titanium alloy is attractive to medical device industry for orthopedic applications, such as total hip replacement systems, fracture fixation plates, intermedullary rods and nails, spinal devices, screws, and wires. Substituting Niobium for Vanadium as the beta stabilizing element, Ti-6Al-7Nb titanium alloy shows higher biocompatability than Ti-6Al-4V titanium alloy. The present research is designed to investigate the influence of annealling temper on the mechanical properties and microstructures of Ti-6Al-7Nb titanium alloy, by optical microscopic (OM) and scanning electron microscopic (SEM), and tensile test. The results show that the microstructures after recrystalization heat treatment comprise a mount of equiaxed α grains in the matrix of equiaxed β phase with α (hcp)/ β (bcc) platelets. The microstructures with partial recrystalization α phase possess better mechanical properties which conform to the ASTM F 1295 standard and ISO 5832-11 standard. Compared with Ti-6Al-4V titanium alloy and CP titanium alloy, Ti-6Al-7Nb titanium alloy is suitable to be used as implanted biomaterial devices to replace ill-functioning or missing tissues or organs.

Abstract: The influences of Gd concentration on martensitic transformation and magnetic properties of NiMnIn alloys were investigated by differential scanning calorimetry (DSC) , vibrating sample magnetometry (VSM), X-ray diffraction (XRD) and etc. It is Observed through the experiment: the addition of Gd enhances martensite transition temperature;X-ray diffraction analysis of experimental alloys is revealed that to the mixture is martensite and austenite at room temperature; content of Gd is not proportional to the improvement of magnetic property.

Abstract: This paper investigates the influence of electrical pulses inoculation and Al-5Ti-B on the as-cast structure of 7075 aluminum alloy. The experimental results indicate that the number of the secondary branch crystal of the solidification structure is effectively controlled, and the feature of as-cast structure achieve the equiaxial and spherical grains after the liquid 7075 Al-alloy was treated by electrical impulse inoculation and Al-5Ti-B. Compared with these samples treating without electrical impulse inoculation, the segregation of Cu and Fe is restrained to a certain extent too. Some primary refinement mechanisms analyze those effects on the solidification structure by treating with electric pulse and Al-5Ti-B; this experiment may provide a theoretical reference for the application of electric impulse in 7075 aluminum alloy.

Abstract: The influences of Gd concentration on martensitic transformation and magnetic properties of NiMnIn alloys were investigated by differential scanning calorimetry (DSC) , vibrating sample magnetometry (VSM), X-ray diffraction (XRD) and etc. It shows that addition of Gd enhances martensite transition temperature and that X-ray diffraction analysis of experimental alloys is revealed which the mixture is martensite and austenite at room temperature. These alloys show promise as a metamagnetic shape memory alloy with magnetic-field-induced shape memory effect.

Abstract: In this paper, preparation of large spray deposited aluminum alloy tube was investigated. The shape and particle size distribution of over-sprayed powders together with structure of deposits were analyzed. The results show that the over-sprayed powders resulted from particles missing, spurting and rebounding. The particle size distribution was non-standard normal distribution, the particle size of the great majority was within 150μm and the average size was 50μm. The residual pores in deposits came into being when inter-particle space could not be filled with enough liquid during spray deposition. The as-deposited preform with rough surface was a coalesced bulk of deposited particles. The rotate speed of substrate and scan speed of atomizer together with spray stripe width should satisfy any certain relationship to obtain a qualified tube preform. Substrate preheating and surface treatment and residual stress control were very important for preparing a large preform.

Abstract: A creep test of the Nickel-based superalloy K403 is performed and the test result shows that the creep deformation under the cyclic load is larger than that under the static load distinctly, which can provide references for the creep deformation analysis of the engine hot parts.