Severe Plastic Deformation to Achieve High Strength and High Ductility in Fe–Ni Based Alloys with Lattice Softening

Abstract

In the present article, recent reports on microstructure and mechanical properties in SPDed FeNiCoTi and FeNiAlC alloys are overviewed. The chemical compositions in these alloys have been determined to have lattice softening where the elastic constant C A goes to a very small value. The alloys with lattice softening were processed with severe plastic deformation, SPD, to raise the strength. Here, SPD includes severe cold working by rotary swaging, cold rolling and high-pressure torsion. These alloys have been reported to have ultrahigh strength along with good tensile ductility and the balance of strength and ductility is better than that in conventional high-strength steels. Microstructural development during the SPD process and the relation between microstructure and mechanical properties in SPDed alloys are summarized. The phase stability of £ has an important role in the microstructural development during SPD process and deformation behavior in the subsequent mechanical testing. The untransformed £ has a potent capability for plastic deformation where strain-induced transformation and deformation twinning can be expected to occur during mechanical tests after SPD processing. Simultaneous activation of these deformation mechanisms during plastic deformation would be a common feature in the lattice softened alloys, but the effects of alloying elements and phase stability on the deformation behavior have not been understood yet.

Advanced Photocatalysts for CO2 Conversion by Severe Plastic Deformation (SPD)

“…The SPD field experienced significant progress in the past three decades, as discussed in several review papers [ 124 , 125 , 126 , 127 , 128 , 129 ], and more recently in a special issue in 2019 [ 130 ], which gathered overviews on both historical developments [ 131 ] and recent advancements [ 132 ]. A survey of these overviews indicates that despite significant progress on theoretical aspects [ 133 , 134 ], mechanisms [ 135 , 136 ], processing [ 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 ], microstructure [ 145 , 146 , 147 , 148 , 149 ], and mechanical properties [ 150 , 151 , 152 , 153 , 154 , 155 ] of metallic materials, there is a recent tendency to apply SPD to a wider range of materials (oxides [ 156 ], semiconductors [ 157 ], carbon polymorphs [ 158 ], glasses [ 159 ], and polymers [ 160 ]) to control phase transformations [ 161 ] and solid-state reaction [ 162 , 163 , 164 ] for achieving advanced functional properties [ 165 , 166 , 167 , 168 , 16...…”

高圧スライド法を用いたTi同素変態のその場放射光X線解析

“…2019 年発行の Materials Transactions 特集号 1,2) では，巨大ひ ずみ加工 (SPD: Severe Plastic Deformation) により，機械的・ 機能的特性が著しく向上することが報告された．SPD の利用 は，多くのレビュー論文 [3][4][5][6][7][8][9][10][11][12] で知られるように，ほとんどが 金属材料であった．しかし，高圧ねじり (HPT: High-Pressure Torsion) 加工と呼ばれる方法を用いて高圧下で操作すること により 13,14) ，金属間化合物 19,20) ，半導体 3,[21][22][23][24] ，セラミック ス 25,26) など延性が低く変形が難しい材料にも利用され [15][16][17][18] ， その適用範囲は拡大することができている．また，HPT 加工 によれば，粉末，チップ，箔体の固化も可能であり，バルク 材料の合成にも応用を広げることができる ．さらに，高 圧相を利用して，機能性を持たせることも可能である [50][51][52][53][54] ． HPT プロセスは 1900 年代初頭に Bridgman によって開発さ れたものである 13,14) ．円盤状試料を上下のアンビル間に置き， 高圧を印加しながら一方のアンビルを他方に対して回転さ せ，強いせん断ひずみを導入するプロセス法である．最近， Fig. 1 のようにアンビル間の相互回転を往復に変更し，高圧…”

Mechanical Properties and Deformation Behavior in Severely Cold-Rolled Fe–Ni–Al–C Alloys with Lüders Deformation —Overview with Recent Experimental Results—

“…Furuta et al designed the alloy composition of Fe24.6Ni 5.8Al0.4C 1) by considering the phase stability, where they controlled the averaged valence electron number to generate lattice softening. 13) Lattice softened alloys, TiNbTaZr O, 1417) and the FeNiCoTi 18,19) base alloys, have been reported to have high strength and high ductility by applying severe plastic deformation. The crystal structure of these two lattice-softened alloys is bcc or fcc, although a part of the specimens transforms during severe cold working.…”

“…However, the relationship between Lüders-type deformation and mechanical properties has not been well understood. 13) We think that clarifying the mechanism for high strength and high ductility with Lüders-type deformation in these steels is essential for the development of novel practical steels with high strength and high ductility.…”