Eş Kanallı Açısal Pres (EKAP) Yöntemi ile Şekillendirilmiş Ti-6Al-4V Alaşımının Mekanik Özellikleri ve Makroskobik Deformasyon Davranışı Arasındaki İlişki

Bu çalışmada, Ti-6Al-4V alaşımının kaba taneli ve eşit kanallı açısal presleme (EKAP) ile üretilen ultraince taneli durumda, quasi-statik tek eksenli çekme yüklemesi altında (yaklaşık 10-3 s-1 deformasyon hızıile) sergilediği mekanik davranış ve makroskobik deformasyon modu (homojen vs. lokalize) karakterizeedilmiştir. EKAP işleminin ve farklı kanal iç açılarının çekme dayanımı, kopma uzaması (süneklik),üniform uzama ve sertlik gibi malzemenin mekanik özelliklerine etkisi kapsamlı bir şekilde incelenmiştir.Dijital görüntü korelasyon (DIC) tekniği ile tüm çekme testleri esnasında yüzey deformasyon alanları insituolarak ölçülmüştür. Çift paso EKAP işlemi sonrası malzemenin çekme dayanımı, akma dayanımı vesertliğinin sırasıyla 795,8 MPa, 660 MPa ve 255 HV’den, 120° kanal iç açılı kalıpla EKAPlanmış numunede918,3 MPa, 850 MPa, 303 HV ve 90° kanal iç açılı kalıpla EKAPlanmış numunede ise 990,5 MPa, 890MPa, 343 HV değerlerine ulaştığı görülmüştür. Ancak, tanelerin EKAP prosesi neticesinde incelmesi,malzemenin müteakip kırılmasını tetikleyebilecek olan erken zamanlı deformasyon lokalizasyonunabağlı olarak üniform uzama ve kopma uzamasında önemli bir gerilemeyi beraberinde getirmektedir. DICverileri, başlangıç numunesinde (EKAP öncesi) deformasyonun homojen olarak ilerlediğini; çift pasoEKAP işlemi sonrası çekme yüklemesine tabi tutulan numunede ise deformasyonun daha ziyadeinhomojen/lokalize bir mod eğilimi sergilediğini açıkça ortaya koymaktadır. Bu çalışma kapsamında eldeedilen sonuçlar, EKAP sonrası plastik deformasyona tabi tutulan malzemenin makroskobik deformasyonmodu ile sünekliği arasındaki ilişkiye dair yeni bakış açıları kazandırmaktadır.

Relationship between Mechanical Behavior and Macroscopic Deformation Mode of Ti-6Al-4V Alloy Processed by ECAP

In this study, the mechanical behavior and the macroscopic deformation mode with respect to localized vs. homogenous deformation under quasi-static uniaxial tensile loading (at the strain rate of about 10-3 s-1) of Ti-6Al-4V alloy in the as-received (coarse-grained) and the ultrafine-grained (UFG) state produced by equal-channel angular pressing (ECAP) are characterized. The effect of ECAP process and different intersecting channel angles on the mechanical properties such as the tensile strength, the ultimate strain (ductility), the uniform elongation and the hardness is studied extensively. Digital image correlation (DIC) is used to document the surface strain fields in situ during all the tensile tests. It is shown that the tensile strength, the yield strength and the hardness of the material increased from 795,8 MPa, 660 MPa and 255 HV to 918,3 MPa, 850 MPa, 303 HV and 990,5 MPa, 890 MPa, 343 HV by applying two passes of ECAP using a mold with an intersecting channel angle of 120° and 90°, respectively. However, a refinement of the grains by ECAP leads to a significant decrease in the uniform elongation and ultimate strain due to the early stage strain localization, which may provide the nuclei for subsequent fracture of the material. DIC-images clearly indicate that in the as-received state, the deformation proceeds homogeneously, whereas after two passes of ECAP, the deformation tends to an inhomogeneous/localized macroscopic mode. The results presented in this work provide new insights into the relationship between the macroscopic deformation mode and the ductility of the ECAPed material.

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