原田 泰典

Sintered molybdenum plate was rolled in one pass at 873 K to specimens with four degrees of 0, 10, 25 and 50% in thickness reduction. Tensile tests for the smooth and notched specimens were carried out to examine the effects of the level of plastic deformation and the edge notch on the change of ductile-brittle transition temperature (DBTT). The specimens were pulled at various temperatures between 163 K and 473 K and at a strain rate of 5.5×10^-3s^-1. Consequently, molybdenum could be deformed without any detectable defect up to 50% reduction in thickness by the rolling. For both of the smooth and notched specimens, the ductile-brittle transition temperatures were monotonously lowered with increasing the thickness reduction. The presence of an edge notch caused an increase of transition temperature by about 120 K to 160 K in a thickness reduction range of 0% to 50%.

Long pure titanium cups were formed by multi-stage cold deep drawing using commercial coloured titanium sheets for preventing seizing. The titanium sheets have sufficient ductility and high r-value for the deep drawing, whereas the seizure tends to occur during the deep drawing due to high reactivity with die materials. The coloured pure titanium sheets were treated by electrochemical coating so as to get oxide surface layer effective for preventing the seizing. By the use of commercial coloured sheets, the investment of coating machines can be avoided in sheet metal forming makers and the quality of the oxide layer can be controlled. The effects of the thickness of the oxide layer, die materials and lubricants on the occurrence of seizure in multi-stage deep drawing were examined. It was found that the coloured pure titanium sheets have sufficient ability in preventing the seizure in multi-stage deep drawing processes.

Feasibility of mushy state forming of magnesium alloys making use of resistance heating was examined. Magnesium alloys, AZ31, AZ61 and AZ91, were taken up as experimental materials and cylindrical billets with a diameter of 15mm and a height of 20 mm were used for both resistance heating and forming experiments. Input heat control was applied to the billet heating and insertion of thin discs of austenitic stainless steel with a low thermal conductivity between the billet and copper electrodes was attempted in order to improve the efficiency of the billet heating. Results were summarized as follows. (1) Resistance heating by input heat control was successful to heat the billets to their respective mushy state. (2) Insertion of the discs was very helpful in heating the billets and realized the heating in a couple of seconds. (3) The force applied to the electrodes to ensure the electrical contacts being too small, sparks occurred and welds arose between the billets and discs. Contact pressure more than 19.6MPa was needed to avoid the welding. (4) Mushy state upsetting in a container with an inside diameter 20mm and extrusion with a right angle die with a hole of 5mm in diameter were both performed with fair success using input heat control.

The present paper provides details on the thermomechanical treatment of chromium-nickel alloys with high content of chromium, which leads to considerable improvement of their mechanical properties. The investigated alloys were prepared from Cr-Ni powder mixtures containing 50% and 80% of chromium in mass. They were formed by a particular sequence of cold and hot isostatic pressing. The as-sintered compacts were essentially brittle at room temperature, while they have exhibited considerable ductility after the special thermomechanical treatments. The treatment consisted of a sequence of repeated rolling and annealing operations, which is relatively simple and applicable in the industrial production. It is found that the treatments led to a more homogeneous, better alloyed structure and enhanced interdiffusion of the component metals. (C) 2002 Elsevier Science B.V. All rights reserved.

The workability of cast pure chromium was investigated through the study of rolling and isothermal upsetting. The present cast block produced by means of a high energy induction slag melting (HESM) process was 99.99 % mass purity and this material had large crystal grains elongated along the solidification direction. The ductile-brittle transition temperature (DBTT) of small specimens taken from the block was found to be about 500 K in a tension strained at 0.024 s(-1). Considerable workability appeared in upsetting at 400 K, at which the small workpiece could be deformed to 25 % in height reduction without cracking on the piece wall. The upsetting workability increased rapidly with increasing temperature, that is, the piece was deformed up to 80 % at 773 K and more than 90 % at higher temperatures than 873 K. At all temperature, cracks occurred in the as-east specimen deformed by a conventional rolling. In addition, cracks occurred slightly in the specimen even in a sandwich rolling by which sintered chromium was successfully deformed. Cracking in the as-cast specimen was mainly due to the coarse structure with large crystal gains. Once the coarse gram structure in the cast material was changed to a finer one by upsetting and successive annealing treatment, the present chromium could be successfully rolled to a thin sheet at temperatures above 673 K.

To improve the surface properties of magnesium alloy, a lining process using shot peening was carried out. The lining of magnesium alloy with metals such as titanium and nickel is useful in heightening the corrosion and wear properties for the components. In the shot peening experiment, the foil set on the magnesium workpiece is pelted with many shots at a high velocity. The foil is bonded to the surface of the workpiece due to plastic deformation induced by the collision of the shots. A pure aluminum foil is inserted between the hard foil and magnesium workpiece to assist the bonding. To heighten the bondability, the foil and workpiece are heated and the flow stresses of the metals are reduced. In this experiment, a centrifugal shot peening machine with an electrical heater was employed. The workpieces were commercially magnesium alloys AZ31B and AZ91D, and the foils were commercially pure aluminum, pure titanium and pure nickel. The effects of collision speed and the processing temperature on the bondability were examined. It was found that the foils were successfully bonded to the surface of workpieces by the shot peening process.

The feasibility of mushy state forming of aluminium alloy making use of resistance heating was examined. Aluminium alloy (A357) was used as an experimental material and billets of rectangular prism with a cross-section 10 mm 2 and height 20 mm were used for heating and forming experiments. Input heat control was applied to the billet heating and the insertion of thin discs of austenitic stainless steel with a low thermal conductivity between the billet and copper electrodes was used in order to improve the efficiency of the billet heating. Results were summarised as follows. (1) Insertion of the discs was very helpful in heating the billet to its mushy state. (2) The force applied to the electrodes to ensure the electrical contacts being too small, sparks occurred and welds arose between the billet and discs. Contact pressure of more than 19.6 MPa was needed at the start of electrification to avoid the welding. (3) Mushy state upsetting in a container and forming with a shaped die were both successfully performed using input heat control. (C) 2002 Elsevier Science B.V. All rights reserved.

A lining of light metals with hard powders using shot peening was carried out. The hard powders are bonded to the surface of the workpieces due to the collision with many shots. To fix the hard powders on the surface of the workpiece, the powder is placed on the uneven surface, and the surface is covered with a pure aluminium foil during the shot peening. To make the fixing of powders easy, the lining of workpiece with the powders sandwiched in between two aluminium foils was also tried. In this experiment, a centrifugal shot peening machine with an electrical heater is employed. The workpieces are aluminium and magnesium alloys, and the hard powders are commercially pure chromium, ceramics and cemented carbide. The effects of collision speed and the processing temperature on the bondability were examined. The wear resistance was evaluated by wear test. The hard powders are successfully bonded over the surface of workpieces by raising the processing temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Chromium is known to have limited room-temperature ductility but to exhibit apparent ductile-to-brittle transition behaviour at temperatures ranging from 150 to 300degreesC. In this paper, the deformation behaviour of a chromium sheet was investigated in roll-compression and laser bending. Tensile tests and three-point bending tests were performed also to determine the basic mechanical properties of the chromium sheet. The ductile-to-brittle transition temperature of the chromium determined by the tensile test was found to be 180degreesC. While the sheet could be bent to 90degrees at a temperature of 130degreesC in three-point bending, it was possible to bend the sheet to the same bending angle at a lower temperature (100degreesC) in roll-compression bending, the presence of compressive stress in roll-compression bending being considered to be the reason for the difference in the temperatures. A finite element stress analysis was also conducted to reveal the stress distribution of the chromium sheet in roll-compression bending. Laser bending was demonstrated to be a possible process to deform chromium sheets. A threshold laser power of 40 W is observed, below which bending is unlikely to occur. The bending angle was found to increase with increasing laser power and number of irradiations, and decreasing scanning velocity. (C) 2002 Elsevier Science B.V. All rights reserved.

Experiments were performed with high purity chromium to make a search for some method for improving the ductility at room temperature. The ductile-to-brittle temperature (DBTT) was about 555 K for as-sintered specimens. However, it was lowered by about 200 K using proper thermomechanical treatment. For example, the rolling at 973 K to reduce the specimen thickness by 15% per pass, and the subsequent annealing at 1273-1373 K were repeated until the total reduction of specimen thickness reached 85%, followed by the final annealing at 1473 K. When such thermomechanically treated specimens were then pre-strained by 2-5%, polycrystalline chromium exhibited a fracture elongation 20% even at room temperature.

Long pure titanium cups with an excellent resistance to corrosion were formed by preventing seizure in multi-stage deep drawing processes of titanium sheets. The titanium sheets have sufficient ductility and high r-vale for the deep drawing, whereas the seizure tends to occur during the deep drawing due to high reactivity with other materials. For the prevention, pure titanium sheets were treated by electrochemical and heating oxide coatings. The effects of the coating methods and conditions and die materials on the occurrence of seizure in the multi-stage deep drawing were examined. Long pure titanium cups with the height which is 6 times larger than the diameter were successfully formed by using bronze dies or oxide re-coating.

High purity chromium powders were sintered into a block by means of hot isostatic pressing. Pieces taken from the sintered block were thermo-mechanically treated, i.e., repeatedly rolled at 973 K up to 50 and 85% in total reduction, with and without intermediate annealing at 1273 K. The ductile-brittle transition temperature, DBTT, was determined by a tension test with the specimens cut from the as-sintered block and the roiled sheets. DBTT for the specimen rolled without intermediate annealing was about 600 K, while DBTT of the specimen rolled with the annealing was 400 K much lower than the above temperature 600 K and the temperature 500 K which was found in the as-sintered material. The reduction in DBTT through the thermo-mechanical treatment probably comes from the decrease of susceptibility to the occurrence of brittle fracture at grain boundaries.

Resistance sintering performance of copper powder mixed with alumina particles was examined, including effect of post-electrification pressing. Simultaneous joining of the composites to a SUS304 stainless steel disk and forming in the sinter process were also attempted from the standpoint of effective use of the heat and pressure. Results obtained were summarized as follows: (1) green compacts containing alumina particle up to 40 mass% were able to be resistance-sintered, and the post-electrification pressing increased the density of the sintered compacts, (2) the simultaneous joining of the composites to the stainless steel was successfully performed when heat input was sufficient, and the post-electrification pressing operated to increase the bond strength, and (3) the simultaneous forming of the composite was possible when the green compact was sufficiently heated under low pressure. (C) 2001 Elsevier Science B.V. All rights reserved.

High purity chromium powders were sintered into a block by a hot isostatic pressing. Pieces taken from the sintered ingot were thermo-mechanically treated, i.e., repeatedly rolled at 973 K up to 50 and 85% in total reduction with and without the intermediate annealing at 1273 K. The ductile-to-brittle transition temperature, DBTT, determined in a tension test was decreased down to 400 K for the specimen of the rolled sheets with the intermediate annealing from the temperature 500 K found in the specimen of the as-sintered material. While, DBTT for the specimen of the sheets rolled without the intermediate annealing was about 600 K. The application of the repeated rolling with the intermediate annealing to the sintered chromium was found to be effective to lower its DBTT.

The feasibility of a resistance sinter-forming method newly designed for parts production of ceramic particle dispersed metal matrix composites was investigated. SiC particle dispersed copper matrix composites were taken up as an example, and basic resistance sintering and sinter-upsetting experiments were conducted using copper powders mixed with abrasive SiC powders. The success of resistance sintering depended on the magnitude of the electrical resistance of mixed powders. The results of resistance sinter-upsetting experiment using a green compact billet strongly depended on electrifying conditions including the applied pressure. Experimental resistance sinter-forging using shaped electrodes was successfully performed, thereby demonstrating a high feasibility of the method.

Small cylindrical billets of sintered chromium and cast one, being very difficult-to-form materials, were isothermally extruded at warm temperatures to examine the effect of pressurization on the workability using two types of dyes, single-reduction dyes and double-reduction ones. Ductile-to-brittle transition temperature determined in tension for the sintered material was somewhat lowered by pressurization at 7,000 to 10,000 atmospheres. Differently from upsetting workability, extrusion workability was poorly improved only for the sintered chromium by pressurization at 10,000 atmospheres. The use of double-reduction dies was advantageous to the decrease in extrusion temperature above which the successful extrusion could be performed.

The Wilms' tumor 1 gene (WT1) is a tumor suppressor gene whose alterations are linked to the genesis of Wilms' tumor. The gene is expressed in the urogenital organs and plays a key role in their development. Recent studies have shown that the WT1 gene product acts as a growth promoter of human leukemic cells. Because WT1 has been reported to be important in testicular development, we have investigated WT1 messenger RNA (mRNA) expression in testicular germ-cell tumors. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to examine the levels of WT1 mRNA in 34 patients with testicular germ-cell tumor, including 25 low-stage and 9 high-stage tumors. There were 23 seminomas and 11 nonseminomas. The WT1 mRNA was highly expressed in 6 of 9 high-stage lesions (67%) but only 5 of 25 low-stage cases (20%). A significant correlation was observed between the extent of WT1 mRNA expression and tumor stage (P = 0.017). There was no significant difference in WT1 mRNA expression between seminomas and nonseminomatous tumors. These results suggest that WT1 may be causal for the progression of testicular germ-cell tumors.

Most testicular germ cell tumors have serological tumor markers such as alpha-fetoprotein (AFP) and human chorionic gonadotropin beta-subunit (beta-HCG). On the other hand, molecular staging of these tumors has not been well established compared to other urogenital malignancies like prostate cancer. Recently, melanoma antigen (MAGE) which is one of the tumor-associated antigens recognized by cytotoxic T lymphocytes (CTL) has been found to be present in a variety of malignant tumor types and normal testis. In addition, Wilms' tumor-associated gene WT1 has been found to be expressed in some testicular cancers. Thus, we examined the expression of these genes in testicular cancer tissues and peripheral blood of cancer-bearing patients using reverse transcription-polymerase chain reaction (RT-PCR). The expression of the MAGE1-3 genes was examined in 34 testicular germ cell tumors (24 seminomas and 10 nonseminomas). Of the seminomas and nonseminomas, 87.5% and 40% were positive for MAGE1, 91.7% and 60% for MAGE2, and 83.3% and 30% for MAGE3, respectively. The expression of the MAGE genes was not correlated with the tumor stage. The expression of the WT1 gene was quantified in 26 testicular germ cell tumors. WT1 was highly expressed in 5 of the 7 high stage cases, but in only 4 of the 19 low stage cases (p < 0.01). The mRNA of these genes could not be detected from the peripheral blood of patients with high stage tumors. These results suggest that MAGE genes may be useful tumor markers for molecular staging of testicular cancer, especially seminoma, and that the WT1 gene may be a tumor marker for high stage testicular germ cell tumors. However, these genes cannot yet be used for molecular staging of testicular germ cell tumors.