Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion

Murat Isik, Mitsuo Niinomi, Huihong Liu, Ken Cho, Masaaki Nakai, Zenji Horita, Shigeo Sato, Takayuki Narushima, Hakan Yilmazer, Makoto Nagasako

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Ultrafine-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (HPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultrafine grains. In this study, the grain refinement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line profile analysis. The microstructure of the CCM alloy subjected to HPT processing (CCMHPT) was evaluated as a function of torsional rotation number, N and equivalent strain, ϵeq. Strain-induced γ→ϵ transformation in neighboring ultrafine grains is observed in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultrafine grains, which suggests the formation of low-angle grain boundaries in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Two possible grain refinement mechanisms are proposed. The maximum dislocation densities, which are 2.8 × 1016 m-2 in γ phase and 3.8 × 1016 m-2 in ϵ phase, and maximum subgrain diameters, which are 21.2 nm in γ phase and 36 nm in ϵ phase, are achieved in CCMHPT processed at ϵeq= 9. HPT processing causes a substantial increase in the tensile strength and hardness owing to the grain refinement and a significant increase in the volume fraction of ϵ phase and dislocation density.

Original languageEnglish
Pages (from-to)1109-1118
Number of pages10
JournalMaterials Transactions
Volume57
Issue number7
DOIs
Publication statusPublished - Jan 1 2016

Fingerprint

Grain refinement
Torsional stress
torsion
Mechanical properties
Processing
Volume fraction
Plastic deformation
mechanical properties
Grain boundaries
Tensile strength
Hardness
X rays
Crystals
Microstructure
Ultrafine
tensile strength
plastic deformation
hardness
grain boundaries
grain size

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion. / Isik, Murat; Niinomi, Mitsuo; Liu, Huihong; Cho, Ken; Nakai, Masaaki; Horita, Zenji; Sato, Shigeo; Narushima, Takayuki; Yilmazer, Hakan; Nagasako, Makoto.

In: Materials Transactions, Vol. 57, No. 7, 01.01.2016, p. 1109-1118.

Research output: Contribution to journalArticle

Isik, M, Niinomi, M, Liu, H, Cho, K, Nakai, M, Horita, Z, Sato, S, Narushima, T, Yilmazer, H & Nagasako, M 2016, 'Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion', Materials Transactions, vol. 57, no. 7, pp. 1109-1118. https://doi.org/10.2320/matertrans.M2016052
Isik, Murat ; Niinomi, Mitsuo ; Liu, Huihong ; Cho, Ken ; Nakai, Masaaki ; Horita, Zenji ; Sato, Shigeo ; Narushima, Takayuki ; Yilmazer, Hakan ; Nagasako, Makoto. / Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion. In: Materials Transactions. 2016 ; Vol. 57, No. 7. pp. 1109-1118.
@article{55c505f8b2274e62a1a46d85c0d05e22,
title = "Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion",
abstract = "Ultrafine-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (HPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultrafine grains. In this study, the grain refinement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line profile analysis. The microstructure of the CCM alloy subjected to HPT processing (CCMHPT) was evaluated as a function of torsional rotation number, N and equivalent strain, ϵeq. Strain-induced γ→ϵ transformation in neighboring ultrafine grains is observed in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultrafine grains, which suggests the formation of low-angle grain boundaries in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Two possible grain refinement mechanisms are proposed. The maximum dislocation densities, which are 2.8 × 1016 m-2 in γ phase and 3.8 × 1016 m-2 in ϵ phase, and maximum subgrain diameters, which are 21.2 nm in γ phase and 36 nm in ϵ phase, are achieved in CCMHPT processed at ϵeq= 9. HPT processing causes a substantial increase in the tensile strength and hardness owing to the grain refinement and a significant increase in the volume fraction of ϵ phase and dislocation density.",
author = "Murat Isik and Mitsuo Niinomi and Huihong Liu and Ken Cho and Masaaki Nakai and Zenji Horita and Shigeo Sato and Takayuki Narushima and Hakan Yilmazer and Makoto Nagasako",
year = "2016",
month = "1",
day = "1",
doi = "10.2320/matertrans.M2016052",
language = "English",
volume = "57",
pages = "1109--1118",
journal = "Materials Transactions",
issn = "0916-1821",
publisher = "The Japan Institute of Metals and Materials",
number = "7",

}

TY - JOUR

T1 - Grain refinement mechanism and evolution of dislocation structure of Co-Cr-Mo alloy subjected to high-pressure torsion

AU - Isik, Murat

AU - Niinomi, Mitsuo

AU - Liu, Huihong

AU - Cho, Ken

AU - Nakai, Masaaki

AU - Horita, Zenji

AU - Sato, Shigeo

AU - Narushima, Takayuki

AU - Yilmazer, Hakan

AU - Nagasako, Makoto

PY - 2016/1/1

Y1 - 2016/1/1

N2 - Ultrafine-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (HPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultrafine grains. In this study, the grain refinement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line profile analysis. The microstructure of the CCM alloy subjected to HPT processing (CCMHPT) was evaluated as a function of torsional rotation number, N and equivalent strain, ϵeq. Strain-induced γ→ϵ transformation in neighboring ultrafine grains is observed in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultrafine grains, which suggests the formation of low-angle grain boundaries in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Two possible grain refinement mechanisms are proposed. The maximum dislocation densities, which are 2.8 × 1016 m-2 in γ phase and 3.8 × 1016 m-2 in ϵ phase, and maximum subgrain diameters, which are 21.2 nm in γ phase and 36 nm in ϵ phase, are achieved in CCMHPT processed at ϵeq= 9. HPT processing causes a substantial increase in the tensile strength and hardness owing to the grain refinement and a significant increase in the volume fraction of ϵ phase and dislocation density.

AB - Ultrafine-grained materials often possess superior mechanical properties owing to their small grain size. The high-pressure torsion (HPT) process is a severe plastic deformation method used to induce ultra-large strain and produce ultrafine grains. In this study, the grain refinement mechanisms in the Co-28Cr-6Mo (CCM) alloy, evolution of dislocation density as a result of HPT and its effects on mechanical properties were investigated. The dislocation density and subgrain diameter were also calculated by X-ray line profile analysis. The microstructure of the CCM alloy subjected to HPT processing (CCMHPT) was evaluated as a function of torsional rotation number, N and equivalent strain, ϵeq. Strain-induced γ→ϵ transformation in neighboring ultrafine grains is observed in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Low-angle crystal rotation around the [110] fcc direction occurs in different locations in the same elongated grain neighboring ultrafine grains, which suggests the formation of low-angle grain boundaries in CCMHPT processed at ϵeq= 2.25 and ϵeq= 4.5. Two possible grain refinement mechanisms are proposed. The maximum dislocation densities, which are 2.8 × 1016 m-2 in γ phase and 3.8 × 1016 m-2 in ϵ phase, and maximum subgrain diameters, which are 21.2 nm in γ phase and 36 nm in ϵ phase, are achieved in CCMHPT processed at ϵeq= 9. HPT processing causes a substantial increase in the tensile strength and hardness owing to the grain refinement and a significant increase in the volume fraction of ϵ phase and dislocation density.

UR - http://www.scopus.com/inward/record.url?scp=84978426191&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84978426191&partnerID=8YFLogxK

U2 - 10.2320/matertrans.M2016052

DO - 10.2320/matertrans.M2016052

M3 - Article

AN - SCOPUS:84978426191

VL - 57

SP - 1109

EP - 1118

JO - Materials Transactions

JF - Materials Transactions

SN - 0916-1821

IS - 7

ER -