Kunio Funami

Manufacturing process and mechanical properties of fine TiB dispersed Ti–6Al–4V alloy composites obtained by reaction sintering

Abstract Fine TiB dispersed Ti–6Al–4V alloy composites were developed using a powder metallurgy method, in which high hardness, high strength, high wear resistance and superplasticity were expected. Boride powder (i.e. TiB2), MoB, CrB and Ti–6Al–4V prealloyed powder were mechanically blended in a high energy ball mill. The powder obtained was pressed into dies and consolidated by reaction sintering. The dispersed boride particles produced reactive TiB in the matrix during sintering. In the hot isostatic press (HIP) which followed, samples showed a very fine microstructure of TiB dispersing homogeneously. At room temperature, hardness, compressive strength and wear resistance had the tendency to increase as blended boride content increases. The results of compressive and tensile test at 1173 K, in the strain rate range of 1×10−3–1×10−4 s−1, showed that TiB dispersed composites exhibited m values of no less than 0.38 and large elongation and superplasticity was confirmed.

Grain refinement and superplasticity of reaction sintered TiC dispersed TI alloy composites using hydrogenation treatment

The purpose of this study is to develop TiC dispersed Ti-6Al-4V alloy composites with useful mechanical properties by using reaction sintered fine TiC dispersion technique in the powder metallurgy method and the hydrogenation treatment due to grain refinement of matrix material. Mo 2 C and Ti-6Al-4V prealloyed powder were mechanically blended in a high energy ball mill. The mixed powder was pressed into dies and consolidated by reaction sintering following HIP treatment. The dispersed particles Mo 2 C produced reactive TiC in the matrix during sintering. In grain refining treatments, hydrogenation, hot roll forming and heat treatment to cause fine dispersed Ti hydride precipitation, and dehydrogenation process were introduced. The result of this fabrication process for controlled grain refinement demonstrate the following: 1) The microstructure of dehydrogenated and recrystallized specimen indicated very fine grain size, less than 3 μ m in diameter. Then, the reacted TiC particles became smaller by hot roll forming after hydrogenation. 2) In Ti-6Al-4V alloy composite with 3vol% Mo 2 C, tensile strength and elongation at room temperature were increased more than 14% in comparison with those of non-hydrogenation. 3) Wear resistance of the developed composite had the tendency to increase as blended Mo 2 C content increased and its superplasticity was confirmed.

Deformation Behavior of Fine Grained Al-Mg Alloy under Biaxial Stress

The grain boundary sliding and the formation of slipped bands and cavitations during biaxial tensile deformation were examined in fine grained Al-Mg alloy. Biaxial tensile testing was conducted with cruciform specimens at initial strain rates of 10-4 to 101s-1. It was found that at the same equivalent strain conditions, the number of cavities under biaxial tension is significantly greater than that under uniaxial tension. A greater prevalence of slipped bands and grain separations were clearly observed under biaxial stress than under uniaxial stress. It was suggested that development of slipped bands resulted from the formation of elongated cavities and multiple deformed bands under biaxial stress. Additionally, the m-value under biaxial stress remained at about 0.3 over a wide range of strain rates. The effects of grain separation and formation of cavities were related to the motion of grain boundary sliding, grain size and loading conditions.

Effect of Grain Size and Microstructure on Appearance of Low Temperature Superplasticity in Al-Mg Alloy

The deformation mechanism and the role of grain boundary sliding (GBS) and intragranular deformation characteristic of low temperature superplasticity (LTSP) were investigated in ultrafine-grained (UFG) Al-Mg alloy using a multi-axial alternative forging technique. In UFG materials, it was shown that elongation and strain rate sensitivity were 340 % and 0.39 respectively at 473 K under a strain rate of 2.8 x 10 -3 s -1 . On the other hand, when grain size exceeded 3 5m, superplasticity did not appear under the same conditions. The main factors affecting the deformation mechanism were investigated based on observations of the microstructure using SEM and TEM. The intragranular deformation contribution, estimated from the aspect ratio of the grains after deformation, was observed to be about 43 %. The appearance of LTSP indicates that the role of intragranular deformation and grain size, together with GBS, were the most important factor.

Biaxial Tensile Deformation Behavior and Microstructural Evolutions of Superplasticity in AZ31 Magnesium Alloy

Magnesium alloys show promise in meeting the demand for materials of lighter weight and higher rigidity. Mg alloys are hard to process and normally require grain refining for improved formability and mechanical properties. To process these fine-grained Mg alloys effectively, it is important to relate their load stress and mechanical properties to changes in their microstructures. Using a biaxial tensile machine and cruciform specimens, to evaluate the mechanical properties, microstructure, and plasticity, in a high temperature biaxial stress state, used of AZ31 Mg alloy sheet. With biaxial deformation, grain boundary slide occurred more frequently than with uniaxial deformation, causing grain boundary separation and formation of micro-voids between the grains. In the vicinity of the cracks and at the locations of grain boundary separation, although deformation temperature at higher than the recrystallization temperature, fine grains (about 2 )m) showing in duplex grain structures were formed locally. The formation of duplex grain structures as a result of local formation of fine grains during the deformation process is a major issue to be solved from the viewpoint of plasticity processing.

Effect of Fine Grain on Mechanical Properties of A6N01 Alloy

The good formability and corrosion resistance of 6N01 Al alloy allow it to be utilized in high-speed train systems, and weight reduction of railway vehicles is possible by improving the strength of this alloy. This study examined the effect of the fine-grained structure on the mechanical properties of the alloy formed by a combination of heat treatment and severe plastic deformation such as forging and rolling. The role of the fine-grained structure in determining the plastic formability was also investigated. The 0.2% proof stress and tensile strength of the heat-treated and multi-axial alternative forging (MAF) processed materials were both greater than 300 MPa. Subsequent cold rolling of these alloys increased both the 0.2% proof stress and tensile strength to over 450 MPa with a grain size of less than 1 μm. The fine-grained structure was confirmed to be effective in improving the strength of the 6N01 Al alloy.

Transition in Deformation Mechanism of AZ31 Magnesium Alloy during High-Temperature Tensile Deformation

Magnesium alloys can be used for reducing the weight of various structural products, because of their high specific strength. They have attracted considerable attention as materials with a reduced environmental load, since they help to save both resources and energy. In order to use Mg alloys for manufacturing vehicles, it is important to investigate the deformation mechanism and transition point for optimizing the material and vehicle design. In this study, we investigated the transition of the deformation mechanism during the high-temperature uniaxial tensile deformation of the AZ31 Mg alloy. At a test temperature of 523 K and an initial strain rate of s−1, the AZ31 Mg alloy (mean grain size: ~5 μm) exhibited stable deformation behavior and the deformation mechanism changed to one dominated by grain boundary sliding.

Grain Refinement and High Temperature Deformation in Friction Stir Processed Sheets of Magnesium Alloys

Grain refinement and high temperature deformation in two kinds of magnesium alloys subjected to friction stir processing (FSP) have been investigated. One was a rolled sheet of LA141Mg and another was a cast plate of AZ91Mg. FSP was developed by adapting the concepts of friction stir welding to obtain a fine grain size in a stirred zone. Grain refinement was achieved by FSP to give fine grain sizes of 11.4μm and 8.4μm for LA141 and AZ91 alloys, respectively. For LA141 alloy, the maximum stress of the FSPed sample was higher than that of the as-received one in the range of 300K to 523K while the elongation to failure of the former was considerably smaller than that of the latter. On the other hand, the elongation for the FSPed sample of AZ91Mg showed three times larger elongation with a lower maximum stress than the as-received cast one at 523K and 2.8×10-3s-1. Further difference in high temperature deformation for both magnesium alloys was discussed based on microstructural change and stress-strain curves.

THE ELECTRO-ELASTIC FIELD OF THE INFINITE PIEZOELECTRIC MEDIUM WITH TWO PIEZOELECTRIC CIRCULAR CYLINDRICAL INCLUSIONS*

The electro-elastic field of the infinite piezoelectric medium with two piezoelectric circular cylindrical inclusions is derived under the antiplane shear stresses and inplane electric fields. The analytical solution is obtained. The proposed method is based upon the use of conformal mapping and the theorem of analytic continuation. From the results obtained, it can be found that the electro-elastic field depends on the material constants of individual phases, the geometric parameters of the system and the applied antiplane shear stresses and electric fields at infinity. In addition, the specific cases when two circular cylindrical inclusions are tangent to each other and they are holes and/or rigid ones, are also studied in this paper.

Influence of Grain Size on Mechanical Properties of AZX311 Alloy

In the present study, the grain refinement, grain growth behavior, and tensile properties of rolled and annealed AZX311 Mg alloys were investigated. The yield strength and ultimate tensile strength of the rolled material were 360 MPa and 370 MPa, respectively, and the total elongation was 5%. When annealing was performed at 423 K for 1hr, the yield strength and ultimate tensile strength were unchanged, but the elongation increased to 10%. Furthermore, the strength and elongation did not change for annealing temperatures of 473–673 K owing to Al2Ca precipitations.