Study Of Structure Refinement And Optimization Of Mechanical Proprieties For Superalloy K4169

Grain refinement has been an available technique for improving the soundness ofsuperalloy structure. It is more imPobot to complicated cornmercial superalloy frompractical and thcoretical views. This present dissertation investigated grain smictureswith addition of refiner comPosed of intermetallic compound for superalloy K4169.The mechanical proprieties were tCsted at room temperature and at modefate hightempertae. The refinement mechanism of superalloy K4l69 and fracforemorphologies were stUdied.The refined structUres of suPeralloy K4169 by addition of trace intermetalliccompounds to the melt were initially obtained under commercial condition with thesame order of grain size obtaned by foreign institutions with thermally controllingmethod. The average size of equiaxed grains could be refined to the order of ASTM1 .7 with the melt homogeneous treatment. Furthermore, the average equiaxed grainscould be refined to ASTM 3.2 without the melt homogeneous treatment. Transversesection of all non-dendrite smictUfCs was achieved.The fined structUres had less dendrite segregation than the coarse grain taes.The segregate ratio of Fe, Nb and Cr were tend to unit with decreases of grain sizes,which suggested more whform distributions of these elements.The propriety testS showed that grain reflnement increased by 24.6% and 9.7%respectively in the yield strength and in ultimatC tensile strength at roomtemperafore, as ductile increased by 31% and section shrink rate increased by 26.9%.The refined grains showed ductile fractUre morphologies; the coarse grains showedbrittle fracture morphologies;Grain refinement produced increases of l4.9% and of 2l.3% respectively in theyield strength and in the tensile strength at 700C, but ductile decreased by 32.4%and section shrink rate increased by 20.7%. The refined grains kept ductile fracturemorphologies and the coarse grains showed brittle fract-Ure morphologies.Fatigue lives of superalloy K4l69 at room temperat'Ure and 700C were comparedfOr the first time. Grain refinement resulted in 2 times fatigue life controlled bystrain in average than baseline material at room temperafore. Grain refinemeof stillkept 2.7 times stran cootfOlled fatigue life in high cycle at 700C than coarser grain,but resulted in a slight decrease in low cycle fatigue.Effects of processing parameters on grain strictures were studied. The lowerpouring tempeate was contriboted tO refinemeni sttucfore regardless of additionor no addition; the refining caPacity of the mixed refiner was superior to the singleone. TOo large or too small sizes of refiner particles produced coarse grains.The refinement mechanism of addition was analyzed with experimental results.Disregistry theory is used to explain the refining effect of single refineL The role ofmixed reflner is attributed to the enlarged effective nucleation temperature range,owing to the result of cooperation of two refiners. The experiment showed that the additions were not developed into crack sources, hence the intermetallic compounds additions used were safe refiners.Since the change of liquid constituent on the surface of addition influenced on nucleation, the segregated energy of solute was initially introduced into the nucleation process and it was analyzed that the segregated energy played dominated role in some case. A nucleus parameter ^(= RT(\ -k)- AG?xr), was suggested todescribe the influence of alloy elements on nucleation.The nucleation with chemical reaction was studied for the first time. By means of the currently wetting theories the effect of the reactive energy and interfacial tension energy on nucleation was investigated and the principles of selecting refiner were concluded.A new conception, the crack propagation tenacity, was introduced to estimate the propagation life in fatigue process. It was proved to be l/>/2 times than Griffifth fracture tenacity. In addition, mechanism of formation of tire trail structure was exam...