FATIGUECRACKGROWTH RETARDATION BY THE NUMBER OF DIFFERENT CYCLES OVER LOADİNG ON EFFECT OF PLASMA NITRIDING

Made of aisi4140 steel ct (compact tension) specimens subjected to plasma nitriding process, temperature of 500°c for 2 hours 50 n2%-50 h2% gas mixture. block over load (ol)the number of cycles on fatiguecrack growth retardation, investigated the effect of plasma nitriding.unnitrided and nitrided specimens, the more the number of cycles of ol increased, the more effect ofthe crack retardation found. the crack retardation by over load cycle numbers1,10, 20, 100 and 1000°f, in unnitrided samples effectively occurred, but nitridedat lower levels.crack growth retardation caused by 3000 the number of cyclesof the block over loading, show edhigher levels occurredon the nitrided samples thanunnitrided.and the over load cyclein 3000 increased. structural and mechanical properties of the samples; investigated using x-ray diffraction, micro hardness testing, scanning electron microscopy, optical microscopy and optical digital imaging tools. digital imagean alysis method was usedto monitorfatigue crack growth.