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A bulk amorphous alloy, Zr54Cu36Al4Be6, was synthesized. This alloy shows a yield strength of ~1.8 GPa and a large plastic strain of ~20.5%, which have hardly been observed in monolithic bulk amorphous alloys. Microstructures of this alloy were observed to investigate the origin of the extraordinary plasticity of the alloy. The alloy exhibited a unique microstructure characterized by atomistic-scale phase separation, which probably stems from the large difference in mixing enthalpy between the binary pairs of Zr-Be and Cu-Be. This paper discusses the effect of atomistic-scale phase separation on the enhanced plasticity of amorphous alloys.

keyword : bulk amorphous alloy, plasticity, phase separation

High-temperature dynamic compressive deformation behavior of Zr-based amorphous alloy and amorphous matrix composite containing ductile β crystalline phases was investigated in this study. Dynamic compressive tests were conducted in the temperature range from room temperature to 380℃ using a compressive Kolsky bar, and then the test data were analyzed in relation to microstructure and fracture mode. Dynamic compressive test results indicated that both the maximum compressive stress and total strain of the amorphous alloy and composite decreased with increasing test temperature because shear bands could propagate rapidly as the adiabatic heating effect was added at high temperatures. Above the glass transition temperature, the total strain decreased more abruptly than that in the temperatures between room temperature and 300℃ according to the appearance of the crystallization of amorphous phases. The maximum compressive stress and total strain of the amorphous composite were higher than those of the amorphous alloy over the tested temperature range because β phases played a role in forming multiple shear bands. These findings suggested that applying the evaluation criteria for mechanical properties measured under room-temperature quasi-static loading could cause risks when Zr-based amorphous alloys were used at high temperatures under dynamic loading conditions.

keyword : Zr-based amorphous alloy, composite, crystallization, dynamic compression kolsky bar, glass transition temperature

The effect of grain size on the tensile strength of Fe-26Mn-2Al alloy has been investigated after changing the microstructure by cold rolling. Microstructures in Fe-26Mn-2Al at room temperature consist of a large quantity of austenite and small quantities of ε and α`martensites. And ε and α`martensites were increased by increasing the degree of cold rolling. With increasing the grain size, the volume fraction of martensite was increased which transformed from the austenite by the cold rolling. While tensile strength was linearly increased with increasing the degree of rolling due to transforming austenite to martensite by deformation, elongation was rapidly decreased at early stage but slowly decreased with increasing the degree of cold rolling. With increasing the grain size, strength and elongation were decreased. This effect of grain size on the tensile strength and elongation is less effective in the specimen cold rolled after solutionizing than the solutionized specimen.

keyword : deformation induced martensite, stacking faults, grain size, tensile strength, cold rolling

It is known that the indentation on rolling contact surface have a marked influence on the fatigue life. And it is also clarified that earlier fracture would be occurred by stress concentration at the plastic lug formed around the indentation during rolling contact fatigue in point contact. In this study, the effects of configuration of indentation on rolling contact surface on rolling contact fatigue life in line contact have been investigated at different slide ratios. The resultant data show that the effects of indentation on rolling contact fatigue are varied with the slide ratio. Size and shape of the indentation at slide ratio of 10% directly influences the resultant fatigue life. However, no effect is found at the slide ration of 0%. XRD analysis shows that the change of residual stress and half-value breadth on rolling contact surface corresponds considerably to rolling contact fatigue process.

keyword : rolling contact fatigue, Line contact, indentation, fatigue Life, X-ray difftaction, slide ratio

The effects of solution heat treatment and aging treatment on dry sliding wear properties for A356/20vol.%SiCp composites have been investigated. Heat treatments were performed on A356/20vol.%SiCp composites for different holding time and temperatures. The results show that changes of heat treatment conditions does not affect wear properties of the composites remarkably, even though it affects the hardness of the matrix alloy. The heat-treated samples exhibited stable friction coefficient values in the range of 0.35~0.40. Through the observations and analysis of the worn surface, worn subsurface and wear debris, wear behavior of heat-treated A356/20vol.%SiCp was examined. In the low applied load region, wear has been occurred mainly by oxidation. With increasing the applied load, MML has been formed on the worn subsurface. Occurrence and initiation of crack in MML has led to delamination. In the higher applied load region, transition from mild to severe wear has occurred.

keyword : aluminium, silicon carbide, composites, sliding wear, heat treatment

The effects of heat treatment on dry sliding wear properties for A356/20vol.% SiCp composites have been investigated. Various heat treatments were performed on A356/20vol.% SiCp composites; solution and/or aging treatment for improving mechanical properties of the materials, and low temperature annealing for improving electrical conductivity of the materials. Wear tests have been performed on as-cast and heat-treated samples. The results show that as-cast samples exhibited better resistance to wear than heat-treated samples. Through the observations and analysis of the worn surface, worn subsurface and wear debris, the effect of heat treatment on dry sliding wear properties for A356/20vol.% SiCp composites has been examined. The decrease of wear properties for heat treatment samples is related with the change of microstructural features such as eutectic Si morphology, decrease of electrical conductivity, and occurrence of interfacial reactions between matrix and reinforcing particles.

keyword : aluminum, silicon carbide, composites, sliding wear, heat treatment

The electrical properties of La(l-x)Sr(x)CoO(3) prepared by conventional solid state reaction were investigated. La(l-x)Sr(x)CoO(3) powder with desired ratio could be obtained by heat treatment for 15h at 1000 in the range of 0≤x≤0.3, but un-reacted compound was detected in the range of x≥0.4. The Seebeck coefficient and electrical conductivity for La(l-x)Sr(x)CoO(3) specimens (0≤x≤0.3) sintered at 1250~ 1350℃ for l0h in air were measured. The electrical conductivity for x=0 specimen increased with temperature, that is, exhibited the typical semiconducting tendency, and the Seebeck coefficient was positive, decreased rapidly with temperature. In the case of x=0.1 specimen, electrical conductivity increased slightly with temperature, showed a maximum value and decreased slightly with temperature, that is, exhibited semi-metallic tendency. On the whole, electrical conductivity for 0≤x≤0.1 specimens would be affected more by cooling rate than sintering temperature. On the other hand, electrical conductivity for x≥0.2 specimens exhibited the typical metallic tendency.

keyword : La(1-x)SrxCoO3, electrical conductivity, seebeck coefficient, conduction behavior

Te-doped CoSb3 was prepared by hot pressing and its doping effects on the thermoelectric properties were investigated. Single δ-phase was successfully obtained by encapsulated induction melting and the subsequent heat treatment at 773K for 24 hours, followed by hot pressing under 60 MPa at 773 K for 2 hours. Tellurium atoms successfully acted as electron donors by substituting antimony atoms and thermoelectric properties were remarkably improved by Te doping. Dimensionless figure of merit was obtained to be 0.80 at 650K for the CoSb2.9Te0.l specimen.

keyword : skutterudite, thermoelectric, doping, hot pressing

DLC(a-C:H) films were deposited on STD11 steel and Si(100) substrates by Pulsed DC PECVD method using Ar and C2H2 gaseous mixture at room temperature. Before the DLC deposition, the a-Si:C:H inter-layer was deposited on substrates using Ar and TMS(Tetra Methyl Silane) source. As deposited DLC films were annealed at 300℃ to 700℃ under ambient air and vacuum conditions during an hour. We observed that DLC films thickness was decreased by hydrocarbon species effusion from DLC surface and creaks formed on surface over 600℃ Furthermore found out that microstructural change of DLC films with an increasing temperature. In Raman analysis, the G peaks position shifted to graphite peak position and I(D)/I(G) ratio increased with an annealing temperature. XPS analysis revealed that carbon bonding structures changed sp3 to sp2 under air and vacuum conditions. Those mean that DLC films by heating up continuously become to "graphite-like" structures. This was related to wear behavior and corrosion resistance properties of DLC films. Wear properties of annealed DLC films under both conditions grew worse with an increasing temperature such as worn out the DLC film. Corrosion resistances of annealed DLC films also were inclined to decreasing by structure changes.

keyword : DLC, annealing, microstructure, wear behavior and corrosion resistance