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The purpose of this work is to investigate the effects of Mo content after cold rolling on the mechanical properties and recrystallization in Zr alloys. Based on the results of prior research work, Zr-1Nb-0.5Sn-xMo-0.1Fe was selected. The alloys were cold rolled with 50% reduction ratio. These alloys were recrystallized, after microstructure, mechanical properties and texture were evaluated. With increasing Mo content, Kearns number and the elongation decreased, but tensile strength increased. Also, with increasing Mo content, recrystallization temperature was retarded and grain size was refined. These facts were due to the effect of precipitation, solid solution of Molybdenum.

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The effects of intermediate annealing on the texture evolution were investigated in Al-6 wt%Mg alloy sheets for automobile application. Intermediate annealing was applied to controll the workability and texture in Al-Mg alloys. Textures were analyzed by using orientation distribution function method(ODF). The difference between ODFs at every manufacturing process was obtained by measuring differential orientation distribution function(DODF), which evaluted textures before and after hot rolling, intermediate annealing and T4 treatment. Intermediate annealing decreased the deformation textures, which had an influence on the development of recrystallization textures during final heat treatment.

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The effects of Mn addition on phase transformation behavior and mechanical properties of Cu-(9-x)Ni-xMn-6Sn alloys were investigated. The microstructure and transformation behavior changed with increasing Mn content and heating temperature. The Mn free alloy decomposed spinodally by aging at 350℃ and followed by formation of a metastable γ′ phase which accompanies the increase of mechanical characteristics with increasing Mn content, however, the γ′ phase disappeared and a stable γ phase was dominantly precipitated. When the specimens were aged above 450℃, equilibrium γ phase formed from the initial stage of transformation without any reaction such as spinodal decomposition and transformation of a metastable phase. Therefore, addition of Mn and increasing heating temperature suppressed the hardening effect of alloy in the early stage of aging, and decreased the tensile strength.

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The main objective of the present investigation is to study the effect of the thermomechanical treatment on the structure-property relationships of 7075 plate. Particular emphasis has been placed on clarifying the origin of the anisotropy of mechanical properties. It shows that the application of thermomechanical treatment improves the microstructure and overall tensile properties of 7075 plate. Grain size becomes finer and the morphology of coarse intermetallic particles become favorable as the 7075 plate is thermomechanically processed. This improvement of microstructure directly influences the tensile properties of 7075 plate. While the thermomechanically treated (TMT) 7075 plate don`t show any significant change in tensile properties with specimen orientation, there exists a large variation of tensile properties, in especially elongation, of heat treated (HT) 7075 plate with specimen orientation. HT 7075 plate in LT orientation has a much lower elongation than that in I. orientation. Detailed fractographic study reveals that poor ductility in LT oriented specimen is due to the large effective grain size and also due to the occurrence of cleavage fracture of coarse intermetallic particles along grain boundaries. In short, it has been found that the application of thermomechanical treatment improves the tensile properties of 7075 plate and it can be directly applied for the alloy processing for forged harts.

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Effect of niobium content on the recrystallization behavior of binary Zr-Nb alloys were studied. The specimens with 0.2, 0.4, 0.8 and 1.0 wt.% of niobium were prepared under various annealing temperatures from 300℃ to 800℃ and times from 300 to 5000 minutes after vacuum arc remelting. The recrystallization behavior was observed by a polarized optical microscope, TEM and micro-vickers hardness tester. The recrystallization temperature of the alloys slightly increased with niobimn content due to increase of activation energy. The grain growth of the alloys with 0.2 and 0.4 wt.% of niobium occured rapidly, however, that of the alloys with 0.8 and 1.0 wt.% niobium were gradually retarded due to precipitation. The hardness of the alloy with a high niobium slightly increased by the precipitation of beta phase after annealing at 800℃.

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Copper-rich Cu-Mn-P-(Sn) alloys were designed to have high strengthes with good electrical conductivities for electrical and electronic applications. Aging characteristics of the alloys showed that an optimum combination of mechanical and electrical properties of the alloy was obtained at the atomic concentration ratio of Mn to P being about 2. The precipitate in an aged Cu-1.11Mn-0.28P (wt%) alloy was identified as hexagonal Mn₂P of C22 crystal structure. The lattice parameters of the precipitate determined from the X-ray diffraction analysis were a=6.084Å and c = 3.472Å.

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The shape recovery behavior in Ni-A1 base shape memory alloy whose ductility is improved with Fe and Mn alloying has been investigated by using DSC, XRD and TEM. On heating, the deformed alloys were experienced a double-stage recovery process before they returned to the original shape : The first-stage recovery occurred at lower temperature and the second-stage recovery take place at higher temperature. Increase of bending or tensile strain affected total shape recovery such that it leaded to an increase of the second-stage shape recovery. The shape re-covery at a higher temperature, i.e., second-stage shape recovery was attributed to the hinderance of β` →β transformation by the dislocations in β` martensite introduced during deformation. Possibly, the elastics stress field associated with dislocations would hinder the motion of β`/β boundary. When the alloys were bended at the same strain the second shape recovery increased with annealing at higher temperature because of the increase of volume fraction of the β` martensite in the alloys consisted of β` martensite and β phase.

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The phases in a high speed steel (HSS) roll and a nickel-grain cast iron (Ni-grain) roll were quantitatively analyzed by Mo¨ssbauer spectroscopy. Particular emphasis was placed on the presence of retained austenite formed during heat treatment. Roll microstructures were examined by using Mo¨ssbauer spectroscopy as well as optical microscopy and X-ray diffraction analysis. In the HSS roll, austenite formed after austenitization disappeared after tempering. However, in the Ni-grain roll, austenite was formed during casting, and a considerable amount of austenite still remained after stress relief treatment at 450℃ for 30 min. From these results, the longer stress relief time or the higher stress relief temperature was suggested in order to remove the retained austenite in the Ni-grain roll. The Mo¨ssbauer analysis data matched well with the microstructures and the X-ray diffraction analysis data, confirming that the Mo¨ssbauer analysis is quite useful for the quantitative phase analysis of the rolls.

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Microstructural evolution and mechanical behavior of cast alloy 718 during creep-rupture were investigated at and above 650℃. It has been found that deformation twin proceeded by the propagation of planar bands at 650℃, 704℃ and 760℃. Cracking was initiated along the interfaces between these twin bands and matrix therefore transgranular fracture observed at the temperature. Creep deformation at and above 704℃ caused precipitation of plate-like δ phase along the band. Precipitation of plate-like δ phase on the band prevented from transgranular crystallographic failure, therefore, intergranular creep failure was observed at and above 816℃. Due to plastic deformation during creep failure at and above 816℃ the δ platelets displayed curved morphology at the failed specimens.

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Machinability of disc drums fabricated by hot forging of an AISI 430F stainless steel was investigated in the present study. Particular emphasis was placed on a role of the microstructural change, which mostly depended on the annealing conditions after forging. In the forged drum specimens, MnS inclusions were highly elongated, and a considerable amount of martensite was found. Three different annealing conditions were adopted on the forged drum specimens in order to completely or partly dissolve martensite. The surface roughness tests were conducted on these specimens and then the test data were compared via hardness and microstructures. Severely elongated MnS inclusions deteriorated machinability, but the specimens containing martensite showed a good machined surface because martensite played a role in free-machining instead of MnS inclusions. These findings suggested that a proper amount of martensite formed during forging and annealing would be beneficial for machining of the 430F stainless steel products.

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