Ultrafine Grain Refinement of Biomedical Co-29Cr-6Mo Alloy during Conventional Hot-Compression Deformation

Abstract

In order to examine the microstructural evolution during hot-compression deformation of the biomedical Co-29Cr-6Mo (weight percent) alloy without the addition of Ni, hot-compression tests have been conducted at deformation temperatures ranging from 1050°C to 1200°C at various strain rates of 10 À3 to 10 s À1 . The grain refinement due to dynamic recrystallization (DRX) was identified under all deformation conditions by means of field-emission scanning electron microscopy/electron backscattered diffraction (FESEM/EBSD) and transmission electron microscopy (TEM) observations. Although the DRX grain size (d) of the deformed specimens considerably decreased with an increasing Zener-Hollomon (Z) parameter at strain rates ranging from 10 À3 to 0.1 s À1 , a grain size coarser than that predicted from the d-Z relation was obtained at strain rates of 1.0 and 10 s À1 . An ultrafine-grained microstructure with a grain size of approximately 0.6 lm was obtained under deformation at 1050°C at 0.1 s À1 , from an initial grain size of 40 lm. The grain refinement to a submicron scale of biomedical Co-Cr-Mo alloys has been achieved with hot deformation by~60 pct due to DRX, in which the bulging mechanism is not operative. The ultrafine grains obtained due to DRX without bulging is closely related to the considerably low stacking-fault energy (SFE) of the Co-Cr-Mo alloy at deformation temperatures.

Dynamic Recrystallization Behavior of Biomedical CCM Alloy with Additions of C and N

“…No martensitic transformation occurred and no thermal " phase existed after cooling, indicating a much more stable phase as compared to that in the CCM alloy without C or N addition, in which over half the phase transformed into " phase by martensitic transformation during a similar rapid cooling process. 13) Although the results are not presented here, after various hot compression processes in the current study, minimal " phase was detected by both XRD and EBSD, indicating the effective stabilization of the phase with the addition of C and N in all cases. …”

“…The mechanical properties were also improved greatly by grain refinement. The dynamic recrystallization (DRX) behavior in this alloy was investigated in detail by Yamanaka et al 7) Their results indicated that the DRX was related to the low SFE of this alloy and the dense planar dislocation structures due to the formation of SFs possibly inducing the grain refinement.…”

“…However, it is well known that Co-Cr-Mo alloys have extremely low stacking fault energy (SFE) even at high temperatures (approximately 22 mJ m À2 at 1273 K as calculated by Yamanaka et al 1) in the case of Co-29Cr-6Mo alloy), because the additions of both Cr and Mo reduce the SFE at temperatures below 1273 K.…”

Optimization of Microstructure and Mechanical Properties of Co–Cr–Mo Alloys by High-Pressure Torsion and Subsequent Short Annealing

“…In fact, CCM alloys with small grain size have been practically used. 5) It has been reported that hot forging 6) can re ne the CCM grains from an initial size of 40 µm to 0.6 µm. 6) However, grain renement to a nano-scale is dif cult to be achieved by the conventional processing methods.…”

Effect of Building Position on Phase Distribution in Co-Cr-Mo Alloy Additive Manufactured by Electron-Beam Melting

“…Studies have been conducted on the control of a microstructure by managing its solidi cation conditions such as the scanning speed of the electron beam, scanning pathway, and energy density 8) . Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys have been widely used as implant materials such as arti cial hip joints and knee joints because they have excellent mechanical properties 9) , wear resistance [10][11][12] , corrosion resistance 13) , and biocompatibility. As further improvement of these properties is demanded, more research has been conducted [14][15][16][17][18][19][20] .…”