| The tensile properties of IN718 in cold rolled conditions and in aged conditions after cold rolling were measured. The results show that for cold rolling reductions less than 30%, cold rolling raises the strength of IN718 in both conditions, but the increase of strength in the latter case is less than that in the former case. The increment of strength during aging treatment decreases as cold rolling reduction increases. When cold rolling reduction is more than 30%, the increment in strength changes little.The effect of cold rolling and heat treatment on properties of IN718 has been investigated. The results show that the IN718 solution-treated at 1040℃after cold rolling and aged has higher strength but more sensitive to notch. Cold rolling reduction has little effect on properties. The IN718 solution-treated at 970℃after cold rolling and aged is not sensitive to notch, and the yield and ultimate strength increase as cold rolling reduction increases. The treatment at 850℃for 10 hours after solution treatment at 1040℃can eliminate the notch sensitivity, but obviously decrease the strength of alloy.Hot deformation behavior of solution-treated IN718 has been investigated by means of Thermecmsater-Z simulator. Hot deformation equation was given to characterize the dependence of peak stress on temperature and strain rate. The apparent activation energy is about 443 kJ/mol. The strain rate sensitivity was determined, and three-dimensional distribution map and contour map of strain rate sensitivity parameter with strain rate and temperature at 0.6 true strain were obtained. The relationship between the recrystallization percentage and temperature for given strain rates was determined, and by the relationship, the dynamic microstructure distribution map at 0.76 true strain was pictured. In addition, hot deformation behavior of IN718 with a lot of needle-shapedδprecipitates has been characterized. The apparent activation energy is about 458 kJ/mol.The effect of aging time at 900℃before deformation on hot deformation behavior of IN718 has been investigated. During deformation at 900℃, theγ″phase precipitated during aging raises peak stress, whereas during deformation above 900℃, theγ″phase does not alter peak stress because of the solution ofγ″phase. Moreover theγ″phase does not affect peak strain. Theδphase decreases peak strain and has a strong effect at lower temperature. Theδphase also decreases flow softening rate, but hardly alters peak stress.The texture evolution of the DC and CC 1100 aluminum alloys during rolling was investigated by X-ray diffraction. The results are summarized as follow.The DC hot band possesses finer deformed microstructure and strongerβfiber rolling texture than the CC hot band. After annealing at 454℃for 3 hours, the DC hot band exhibits finer recrystallized grains and stronger cube recrystallization texture than the CC hot band.The relationship between the texture volume fraction and true strain can be quantified by using equations of the JMAK type. The ki value in these equations reflects the rate of formation or disappearance of each texture component.The laser thermal shock and fatisne technique has proved to be a reliable and very flexible method in material testing. Laser beam allows the thermal cycling of relative large components or of their selected areas like junctions, welding, coatings, repaired zones or details relevant for the specific application. Speeding up the life time prediction procedure, compared to conventional approaches, is also possible. Preliminary tests performed by the developed system on various materials and components confirm the versatility of this technique. The maximum thermal tensile stress appears on the irradiated surface just outside laser beam. The maximum thermal compressive, stress appears on the laser beam centre of the irradiated surface. The maximum temperature gradient takes place on the beginning and end of laser beam heating, the surface maximum temperature approaches to equilibrium after the end of laser irradiation within 2-3 seconds.It was proposed for the first time in this thesis that the grain grade of metal materials could be measured by laser thermal shock technique and that thermal shock resistance could be characterized by thermal shock toughness. IN718 superalloy exhibits the cycling softening characteristics during laser thermal fatigue, which is in a good agreement with the conventional experimental results. Thermal fatigue crack initiates in the grain boundary, slipband, carbide and triple-point grain corners. Different crack growth mechanisms were found to drive the crack, in some cases, microcracking and subsequent linking were dominant and other cases pure shearing. The wedge crack forms as a result of grain boundary sliding.
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