Preferential Dynamic Grain Growth Mechanism Enabling the Control of Microstructure and Texture by High Temperature Deformation: Experimental Evidence and Applicability

Abstract

The relationship between the mechanism of high temperature deformation and the evolution behavior of microstructure and the texture during deformation, which has been found in various solid solution alloys, is clarified. It is shown that the preferential dynamic grain growth (PDGG) mechanism proposed by the authors can explain the behavior of microstructure change as well as texture change of all studied alloys without contradiction. The essential aspect of the PDGG mechanism is the preferential growth of crystal grains with the orientation stable for deformation and with low Taylor factor in the given deformation mode. It is concluded that the Taylor factor corresponds to dislocation density and stored energy during the high temperature deformation of solid solution alloys when viscous glide of dislocations is the rate controlling process. The possibility of the occurrence of the PDGG mechanism in materials other than solid solution alloys is also discussed.

Effect of Al Concentration on Basal Texture Formation Behavior of AZ-Series Magnesium Alloys during High-Temperature Deformation

“…Fukutomi et al suggested that the texture orientation in the Al–Mg alloy formed after deformation is associated with a low Taylor factor [ 9 ]. The Taylor factor is determined by the number of slip systems contributing to the deformation.…”

“…Specifically, this value corresponds to the six perfect-pyramidal II slip systems. Because the cross-slip systems, owing to the SFE, provide dislocation paths, their activation seems to contribute to the increase in the Taylor factor [ 9 ]. This implies that a non-basal texture component can develop in AZ31, the component most similar to that of the pure state.…”

“…Fukutomi et al investigated the texture formation behavior of Al–Mg system alloys that have an FCC structure and different magnesium concentrations during high-temperature uniaxial compression. From the texture measurements, including X-ray diffraction (XRD) and electron backscattered diffraction (EBSD) results [ 7 , 8 , 9 ], the following phenomena were observed: (1) Deformation was accompanied mainly by dislocations, and variations in factors, such as the strain rate and deformation temperature, made the Al alloy have textures in specific orientations rather than in random directions; (2) A different magnesium concentration in the alloy affected the intensity of the texture after the deformation process; and (3) The orientations were stable and hardly changed during the high-temperature compression deformation. Similar behaviors were also observed in the results of Fe–Si alloys with BCC structures [ 10 ].…”

Influence of Tensile Stress during Annealing on Primary Recrystallization Texture Development in Fe-3%Si Alloy

“…Fig.14 に，850℃にて一次再結晶焼鈍した後に常温引張試験した試料の結晶方位マップおよび KAM マップを示す。{111}<112>方位粒は{411}<148>方位粒よりも KAM 値が高い ことが確認された。一般的に，加工により蓄積される歪量は結晶方位により異なり21- 23,25,26,28) ，Taylor 因子が関係することが知れているが[21][22][23]25,26) ，今回の結果は，引張変形に 対して{111}<112>方位粒は{411}<148>方位粒よりも歪が蓄積しやすい結晶方位であること を示唆するものと推察される。一方，いずれの方位粒においても，結晶粒径が小さいほど KAM 値が高い傾向が認められた。さらに，粒内の KAM 値分布も均一ではなく，粒界近 傍にて KAM 値が高い傾向が確認された。これは，6%程度の変形量においては，粒内より も粒界近傍の不均一変形領域で転位が堆積しやすい傾向が顕著であるためと推定される。 前項までの考察に使用した Average Misorientation は，各粒における KAM 値の平均値であ り，小さな結晶粒ほど粒界近傍領域の占める割合が大きいため，粒界の影響を受けやすい と考えられる。{111}<112>方位粒は，相対的に粒径が小さいことも影響して他の方位粒よ り歪が蓄積されやすく，850℃の高温においても同様の現象が生じたと推察される。な お，850℃での張力焼鈍後の伸び調査において，張力焼鈍前に 850℃にて焼鈍する条件に おいて伸びが小さい傾向が確認された。Fig. 14 は常温引張試験の結果であるが，高温引張…”