原田 泰典

Cladding is the bonding together of dissimilar metals. One of clad products is the titanium clad steel sheet. It is effective to cover with pure titanium sheet to improve the corrosion resistance of the steel sheet. Titanium clad steel sheets are often achieved by rolling sheets together under high pressure. In the current study, the blank comprising three laminar non-bonded sheets, such as the titanium/steel/titanium sheet, is arranged in the die. The formability of pure titanium clad sheet by multistage deep drawing was investigated to enhance corrosion resistance of steel cup. In the experiment, the blanks were pure titanium sheets JIS1-TP270, JIS2-TP340, ultralow-carbon steel SPCC, and stainless steel SUS316L. The initial thickness of the sheet was 0.2 to 0.5 mm in thickness. The blank diameter was 70 mm. The blanks are merely adjacent sheet however, not joined with each other. In the deep drawing process, a hydraulic press was used in the experiment and the forming speed for the press was about 10 mm/min. The lubricant used was the solid powders of molybdenum disulfide. For the prevention, pure titanium blank was treated by oxide coating. The conditions of heat treatment were annealed at 973 K for 3.6 ks to 7.2 ks. By oxide coating, the titanium sheet has sufficient ability in preventing the seizure in multistage deep drawing. The drawn cups of the three-layer laminated sheet were formed. The seizure did not cause. The oxidatively-treated titanium sheets have sufficient ability in preventing the seizure. In addition, the clad cups until the sixth stage were formed by multistage deep drawing. Long clad cups were successfully formed in multistage deep drawing process.

Aiming to enhance functionality of titanium cup, the formability of titanium/resin/titanium laminated sheet by deep drawing was investigated. Although pure titanium has excellent corrosion resistance, the density of titanium is higher than that of light metals, such as aluminum and magnesium. Part of the titanium cup made of resin allows for weight reduction of the cup. Furthermore, the clad cup is more likely to have heat retention and protection against vibration characteristics. In the experiment, the materials were pure titanium and polycarbonate. The initial thickness of the sheet was 0.2 to 0.5 mm in thickness. A total plate thickness of the blank was 1.0 to 1.5 mm in thickness. The blank diameter is 70 mm. The laminated sheet was constituted by interposing resin between two titanium sheets. Each sheet in stacked condition was not joined each other. In the deep drawing process, the laminated sheet was employed and a flat sheet blank was formed into a circle by a punch. For the prevention of seizure in contact area between a drawing tool and titanium, titanium blank was treated by oxide coating. By this method, the fresh and clean titanium is not in direct contact with the die during the forming due to the existence of the oxide layer. The deep drawing was carried out to investigate the formability. The laminated sheet was successfully drawn without the cracks. The section of the drawn cup was observed to examine a formability of the resin sheet. The reduction rate of the thickness was less than 10%. It was found that the titanium/resin/titanium clad cup was successfully drawn.

ばね鋼にマイクロショットピーニングを施し，硬さや表面粗さなどの表面特性について調べたのち，疲労限度や破面観察などの疲労特性に及ぼす投射条件の影響について調べた．ショットピーニングは空気式機械を用い，投射材は鋳鋼製および超硬合金製の微粒子を用いた．ショットピーニングを施した試験片に対して，硬さ試験や疲労試験などを行った．マイクロショットピーニングはばね鋼の表面粗さや表面硬さなどの表面特性および疲労強度の改善に有効であり，とくに超硬合金製投射材によるピーニング効果が高いことを明らかにした．

Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. However, peeling of the coating material may occur under harsh environments such as high and low temperatures and high humidity with the conventional coating techniques. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was mainly investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloys. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on the magnesium alloy.

Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. However, peeling of the coating material may occur under harsh environments such as high and low temperatures and high humidity with the conventional coating techniques. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was mainly investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloys. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on the magnesium alloy.

This paper deals with the effect of shot peening on the bending strength of an AZ31 magnesium alloy pipe. Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. AZ31 alloy is the most widely used commercial magnesium alloy. In our experiment, extruded pipes of 22 mm O.D., 18 mm I.D., and 2 mm wall thickness were used. Shot peening treatments were applied to the surface of the workpiece using an impeller-type or an air-type peening machine. Tensile and compressive tests were carried out under axial load at a crosshead speed of 10 mm/min, and bending strength tests were performed at a crosshead speed of 100 mm/min under lateral load using an Instron-type testing machine. In the bending tests, the peened workpiece could withstand higher bending yield load. The surface layer of the peened workpieces was also observed by electron backscatter diffractometry (EBSD). It was found that multiple deformation twins were formed during shot peening. The results of the present study revealed that the compressive yield stress of shot-peened pipes is strongly related to their bending strength.

The prediction of formability of titunium is more difficult than steels since its strong anisotropy. If computer simulation can estimate the formability of titanium, we can select the optimal forming conditions. The purpose of this study was to acquire knowledge for the formability prediction by the computer simulation of the square cup deep-drawing of pure titanium. In this paper, the results of FEM analsis of pure titanium were compared with the experimental results to examine the analysis validity. We analyzed the formability of deep-drawing square cup of titanium by the FEM using solid elements. Compared the analysis results with the experimental results such as the forming shape, the punch load, and the thickness, the validity was confirmed. Further, through analyzing the change of the thickness around the forming corner, it was confirmed that the thickness increased to its maximum value during forming process at the stroke of 35mm more than the maximum stroke.

This paper deals with the effect of shot peening on the bending strength of an AZ31 magnesium alloy pipe. Magnesium alloy has a wide range of application prospects in the automobile and electronic industries. AZ31 alloy is the most widely used commercial magnesium alloy. In our experiment, extruded pipes of 22 mm O.D., 18 mm I.D., and 2 mm wall thickness were used. Shot peening treatments were applied to the surface of the workpiece using an impeller-type or an air-type peening machine. Tensile and compressive tests were carried out under axial load at a crosshead speed of 10 mm/min, and bending strength tests were performed at a crosshead speed of 100 mm/min under lateral load using an Instron-type testing machine. In the bending tests, the peened workpiece could withstand higher bending yield load. The surface layer of the peened workpieces was also observed by electron backscatter diffractometry (EBSD). It was found that multiple deformation twins were formed during shot peening. The results of the present study revealed that the compressive yield stress of shot-peened pipes is strongly related to their bending strength.

The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.

近年，金型などの大きな負荷のかかる工業製品に対する長寿命化の要求が高まっている．低い製作コストで長寿命化を図るためには必要部分にのみ高強度な合金被膜を形成する方法が有効と考えられ，本研究ではレーザ熱処理を用いて炭素鋼表面に局所的なFe-Al系合金被膜を作成する手法を提案する．ショットライニングにより炭層鋼に貼り付けたアルミ箔にデフォーカスしたCO<sub>2</sub>レーザ照射することで境界面での鉄とアルミの相互拡散を促進しFe-Al系合金を成長させる．生成されるFe-Al系合金の組成は熱処理温度に依存するため，いろいろな熱処理条件でレーザを照射した試験片の断面を観察した結果，高速度レーザ走査によって表面を加熱することで母材の性質を変えずに局所的にFe-Al系合金被膜を生成できることを示した．

The influence of shot peening on the fatigue strength in an extruded magnesium alloy AZ80 treated with T6 was investigated and its anisotropic behavior was discussed. The specimen was machined from different orientations in as-extruded rod. One was loaded in the transverse direction (T specimen). The other was loaded in the longitudinal direction (L specimen). The arc height value of shot peening was set to 0.15 and 0.40 mmN. The specimen surface became rough and hardness became high with an increase in the arc height value. Irrespective of specimen orientation, shot peening at low arc height value improved the fatigue strength. However, the shot peening at high arc height value did not improve the fatigue strength. The same tendency appeared in the case of T4-treated sample, suggesting that precipitation did not affect the fatigue strength degradation by hard shot peening. To investigate the influence of surface roughness formed by shot peening, fatigue tests were conducted using some specimens polished after shot peening. In the L specimen, the polishing after shot peening improves the fatigue life significantly. Therefore, the surface roughness formed by shot peening is one of the important factors in fatigue strength of shot-peened specimen. On the other hand, the fatigue life of T specimen decreased by polishing after shot peening. It was suggested that microstructural damage induced by shot peening decreases the fatigue strength in T specimen.

This paper deals with the formability of pure titanium sheet in square cup deep drawing. Pure titanium has very excellent corrosion resistance. In the metal forming process, pure titanium has very good ductility in cold forming. The normal anisotropy of pure titanium is very high. Therefore, the property is suitable to the sheet metal forming, such as deep drawing process. However, the most important problem is that the occurrence of seizure becomes remarkable in severe forming operations. Many investigations on the effect of processing conditions on the seizure of titanium were carried out. In the present study, the formability of pure titanium sheet in square cup deep drawing was investigated. For the prevention, pure titanium sheets were treated by heat oxide coating. The fresh and clean titanium is not in direct contact with the die during the forming due to the existence of the oxide layer. The material was pure titanium sheets of the JIS grade 2. The initial thickness of the blank was 0.5 mm in thickness. In the deep drawing process, the sheets were employed and a flat sheet blank is formed into a square by a punch. Forming of sheet by multi-stage deep drawing was tried. Various cups were drawn by exchanging the punch and die. The die was taper without a blankholder in the subsequent stages. The effects of the intermediate annealing and tool shape on the occurrence of seizure in square cup deep drawing were also examined. The square cups were successfully drawn by heat oxide coating. The coating of titanium sheet has sufficient ability in preventing the seizure in multi-stage deep drawing operation. The results of the present study revealed that the pure titanium square cups were successfully formed by using heat oxide coating treatment.

Recently, the demand for long life to industrial products has risen. The high strength alloy coating on necessary part can decrease a manufacturing cost for life prolongation. This study proposes a laser surface alloying method to form an Fe-Al alloy coating on a carbon steel. By laser heating to an Al foil stuck on the steel, the mutual diffusion proceeds and the Fe-Al alloy grows. The material property of the generated alloy is greatly different according to a heat treatment temperature. For example, Fe3Al grows at 950 °C or more, and it has high toughness. A furnace heating effects the properties of inside of base material negatively. A high-frequency heating is not suitable for a local surface reforming. The laser processing is suitable for a local surface reforming. A defocused CO2 laser was irradiated to the Al foil stuck on the steel block by the shot lining in various processing conditions. The metal structures of the laser irradiated area was observed, to search for the suitable processing conditions for alloy coating. It was clarified that a local Fe-Al alloy coat was able to be formed without change of the properties of base material by high speed laser scanning.

Aiming to expand the use of the product, the formability of pure titanium sheet by square cup deep drawing was investigated. Forming of titanium sheet was tried by multistage deep drawing. In the experiment, the material was pure titanium sheets of the JIS grade 2. The initial thickness of the blank was 0.5mm in thickness. In the deep drawing process, the sheets were employed and a flat sheet blank is formed into a square by a punch. Various cups were drawn by exchanging the punch and die. The die was taper without a blankholder in the subsequent stages. For the prevention, pure titanium sheets were treated by heat oxide coating. The fresh and clean titanium is not in direct contact with the die during the forming due to the existence of the oxide layer. The effect of the plastic anisotropic on the occurrence of seizure in square cup deep drawing was also examined. The square cups were successfully drawn by heat oxide coating. The coating of titanium sheet has sufficient ability in preventing the seizure in multistage deep drawing operation. It was found that the square pure titanium cups were successfully formed by using heat oxide coating treatment. (C) 2014 Published by Elsevier Ltd.

This paper deals with effect of temperature on stretchability of anisotropic AZ31(Mg-3% Al-1% Zn) magnesium alloy sheet. Results of stretching process test are compared with those of tensile test. The sheet has an anisotropic character for angle to hot-extrusion direction(phi=0 degrees, 45 degrees, and 90 degrees). Here, phi=0 degrees means a direction of extrusion. Tensile specimens cut down to three directions of phi=0 degrees, 45 degrees, and 90 degrees are a shape of 14mm in elongation, 3mm in width and 0.44mm in thickness. Test piece for investigating the limiting stretching stroke is a sheet of side length 90mm and 0.44mm in thickness. For the stretching process test, the punch head is a hemispheric shape of 20mm in diameter and the die is a cylindrical shape of 27mm in inside diameter. Both tension and stretching process tests were performed at four kinds of test temperature(T=293, 393, 473, and 573K) in a thermostatic chamber and at a crosshead speed(v) of 5 mm/min using an Instron-type testing machine. Comparing the limiting stretching stroke determined by the stretching test with elongation, r-value, and n-value obtained by the tensile test, it is confirmed that the limiting stretching stroke is qualitatively related to the elongation and r-value, and not to n-value. (C) 2014 Published by Elsevier Ltd.

Shot peening is widely utilized to improve the fatigue property of mechanical parts for transportation equipment such as cars and airplanes. Also, this technology is being applied as a film-forming technology in order to improve surface quality. The authors have recently proposed new joining methods using shot peening, shot lining. In this method, the metals are bonded with the dissimilar metal by applying plastic deformation and the pressure. The thin foil can be joined to the substrate surface by the pressure generated by the hit of the shots. In this study, the formation of an Fe-Al intermetallic compound film on high-speed tool steel by shot lining and heat treatment was investigated. In the experiment, a centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial high-speed tool steel JIS-SKH51, and the foil was commercially available pure aluminium. The shot lining process of tool steel with an aluminium foil was carried out at 573K in air using a peening machine. Heat treatment was performed at diffusion temperatures from 923 to 1573K in vacuum. The lined substrates exhibited a harder layer of aluminium-rich intermetallics in the diffusion temperature range of 923 to 1173K. When the temperature of the lined substrates was more than 1273K, the surface was covered with thicker and highly anticorrosive layers of iron-rich intermetallics. We found that the present method could be used for the formation of functional films on high-speed tool steel. ? (2014) Trans Tech Publications, Switzerland.

The improvement of formability has been investigated in the multistage deep drawing of beta titanium alloy sheet. The beta titanium alloys have good cold workability in the metal forming. However, a seizure tends to occur during metal forming due to high reactivity with other metals. The occurrence of the seizure becomes remarkable in sever forming operations such as deep drawing and ironing. Especially, it is hard to prevent the occurrence of seizure in multistage deep drawing process. In this study, to improve the formability of titanium alloy sheet, the formability in multistage deep drawing process of beta titanium alloy was investigated. The blank used was the commercial beta titanium alloy Ti-15V-3Cr-3Sn-3Al. To prevent the occurrence of seizure, the blank treated by oxide coating was used. The coated sheet was not in direct contact with the tools of die and punch during deep drawing due to the existence of the oxide layer. The effects of the surface roughness and hardness on the formability in the multistage deep drawing processes were examined. The improvement of surface roughness of drawn cup was also attempted by using heat treatment. A long titanium alloy cup was successfully formed by intermediate annealing at the 3rd stage. The drawn cup by multistage deep drawing could be formed to the 6th stage. It was found that the beta titanium alloy sheet covered with oxide layer has sufficient ability in preventing the seizure in multistage deep drawing processes. (C) 2014 Published by Elsevier Ltd.

The influence of functionally graded TiN coating on the fretting fatigue behavior of titanium alloy was investigated. The coating was deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. TiN film was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment. An acceleration voltage of ion beam was set at 0.2 or 2.0 keV. The functionally graded layer was fabricated by increasing the mixing ratio of nitrogen/argon ion beam. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesive strength and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer improved them significantly. The fretting fatigue live were evaluated by a four-point bending fatigues tests. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life.

The effect of microshot peening on the surface characteristics and fatigue life of spring steel SUP9 was investigated. In the experiment, the projective method of the microshot was of the compressed air type. The microshot of 0.1 mm diameter was high-carbon cast steel, and the workpiece used was the commercially spring steel JIS-SUP9. The effect of the intermittent shot peening on the surface hardness was also studied. The surface layer of the workpiece was sufficiently deformed by microshot peening. The microshot peening process was very efficient in improving the fatigue life of spring steel. It was found that the use of the microshot was found to cause a significantly enhanced peening effect for spring steel. (C) 2014 The Authors. Published by Elsevier Ltd.

In shot peening, bombarding the surface with steel shot propelled at high velocity causes plastic deformation of surface. The process with the characteristic deformation was applied to joining process. Our approach has been applied to the butt joining of the dissimilar metal sheets. In this method, however, the joint strength was lower than the flow stress of base metal. The modified joining processing was being carried out to improve the bondability. In the present study, the joining of dissimilar metal sheets using a shot peening process was investigated to improve the bondability. In the joined section, the edge of the joint area of the sheets were slit using a laser. In this method, the edges of the sheet are overlapped the other sheet. When the connection is peened, the material undergoes large plastic deformation near the surface due to the collision of shots. In this process, particularly noteworthy is the plastic flow near surface layer. The edges of the sheet are joined to the other sheet, thus two sheets can be joined each other. In the experiment, the shot peening treatment was performed by using an air-type peening machine. The shots used were made of high carbon cast steel. Air pressure was 0.6 MPa and peening time was in the range of 30-240s. The metal sheets were commercial low-carbon steel, stainless steel, pure aluminium, aluminium alloy, and pure copper. The effects of processing conditions on the bondability were mainly examined. It was found that the present method was effective for joining of dissimilar metal sheets.

The shot peening process is a widely used surface treatment method for improving fatigue strength and anti-wear characteristics. The surface of the material receives a so-called peening effect where strong local deformation forms a work-hardened layer or causes compressive residual stress. In the present study, the effect of shot peening on fatigue strength of high-toughness spring steel was investigated. The optimum conditions were evaluated in an experiment using the conventional shot peening machine with shots of an average size. The projective method of the shot media was of the centrifugal peening type. The shot media of 1.0 mm diameter was high-carbon cast steel, and the workpiece used was the commercially spring steel JIS-SUP10. The effects of peening time have primarily on surface characteristics and fatigue strength were studied. Fatigue tests were carried out in a plane-bending test machine. S-N curves were established for unpeened and peened conditions. The main results were as follows: the surface layer of the workpieces was sufficiently deformed by shot peening. The residual stress was added in the surface vicinity on all peened workpieces. As the peening time increased, the region with residual stress extends in the depth direction. The value of maximum compressive residual stress was about 950 MPa. At a large number of cycles to fracture, shot peening could more effectively enhance the fatigue strength. When shot velocity was 60 m s-1, the maximum fatigue strength was about 525 MPa with a peening time of 90 s. This peening time was nearly equal to the full coverage time. It was found from the present experiment that the optimum peening time for the conventional shot peening was about 90 s. Shot peening using conventional cast steel shots is conducted for the purpose of improving the fatigue characteristics of spring steel. To examine the effect of shot peening on fatigue strength, fatigue tests are carried out in a plane-bending test machine. It is found that the full-coverage time, 90 s, is required in order to improve the fatigue life. © 2013 WILEY-VCH Verlag GmbH &amp Co. KGaA, Weinheim.

The Mechanical property of free-standing Cu/Al_2O_3 multilayer thin film was investigated by a method of micro-bending test. The Cu and Al_2O_3 monolayer thin film and Cu/Al_2O_3 multilayer thin film were deposited on Si substrate by an electron beam deposition. Free-standing micro-beam specimens were fabricated using a focused ion beam system. The micro-bending tests were conducted using a nanoindenter. Young's moduli of free-standing thin films were estimated by FE analysis including indentation displacement. Young's moduli of Cu and Al_2O_3 films were relatively close to those of bulk material, and that of Cu/Al_2O_3 film with 20 layers was between Cu and Al_2O_3 films. On the other hand, the fracture strength of Cu/Al_2O_3 film with 20 layers was larger than that of Al_2O_3 film.

The Mg-Li alloy which is a beta type alloy was subjected to cold deep drawing, and the formability of Mg-Li alloy sheet was investigated by the square cup deep drawing process. This alloy is about 20 % lighter than a practical alloy. The square cups of magnesium alloy were formed at ambient temperatures. The material was the beta type alloy, Mg-14%Li-1%Al. The initial thickness of the blank was 0.5 to 1 mm in thickness. In the deep drawing, the Mg-Li alloy sheets were employed and a flat sheet blank is formed into a square by a punch. Also, the formability of the Mg-Li alloy was examined by multi-stage deep drawing. Various cups were drawn by exchanging the punch and die. The die was flat in the first stage, and was taper without a blankholder in the subsequent stages. It was confirmed that the Mg-Li alloy square cups were successfully formed by cold deep drawing.

This paper deals with effect of shot peening on bending strength of cylindrical pipe of AZ31(Mg-3%Al-1%Zn) magnesium alloy. Specimen shape of the pipe is 240mm in gauge length and 330mm in total length, 22mm and 18mm in outer and inner diameters. Shot peening treatments were given on the surface of the pipe using an impeller-type peening machine and/or an air-type peening machine. Tensile and compressive tests were carried out under axial load at a crosshead speed of 10mm/min. Bending strength test was also performed at a crosshead speed of 100mm/min under lateral load using an Instron-type testing machine. From the experimental result, the bending yield load of the pipe was strengthened after shot peening treatment. It was found that the compressive yield stresses of the shot-peened pipe were strongly related to their bending strengths.

The formation of an Fe-Al intermetallic compound film on hot work tool steel by shot lining and heat treatment was investigated. In the shot lining method, the metals are bonded with the dissimilar metal by applying plastic deformation and the pressure. The effect of heating temperature on intermetallic formation of aluminum and base material bonded by the lining method was studied. In the experiment, a centrifugal-type peening machine with an electrical heater was employed. The shot lining process of hot work tool steel with an aluminum sheet was carried out. Heat treatment was performed at diffusion temperatures from 973 to 1373K in vacuum. When the temperature of the lined substrates was more than 1173K, the surface was covered with highly anticorrosive layers of Fe-rich intermetallics. It was confirmed that the present method could be used for the formation of functional films on hot work tool steel.

航空機や自動車などの搬送機器では軽量化が進められているため，構成する機械部品である歯車やばねなどにおいても薄肉化や小型化が行われており，より高強度かつ高耐久性のある製品が強く求められている．耐久性を改善できる表面処理法の一つとして，ショットピーニングが広く用いられている．本研究では，これまでにほとんど研究が行われていない高じん性ばね鋼へのマイクロショットによる加工を行い，おもに耐久性向上に影響のある圧縮残留応力に及ぼす投射条件の影響について調べた．投射材は平均直径0.1mmで，比較的新しい超硬合金製および汎用鋳鋼製である．空気式機械を用い，投射圧力0.4〜0.8MPaと投射時間5〜60sの加工条件で行った．その結果，最表面における圧縮残留応力は投射時間を増加させてもあまり変化がないことがわかった．一方，材料内部における圧縮残留応力は投射時間が長くなるにつれて減少したが，材料内部の深い位置まで付与することがわかった．また，表面特性や疲労限度に及ぼす投射材の影響において，超硬合金製による加工の有効性が見られ，材料内部深くまで圧縮残留応力の付与が可能であることや高い疲労限度が得られることがわかった．