Structural evolution of oxide dispersion strengthened austenitic powders during mechanical alloying and subsequent consolidation

    Structural evolution of oxide dispersion strengthened austenitic powders during mechanical alloying and subsequent consolidation Man Wang, Hongying Sun, Lei Zou, Guangming Zhang, Shaofu Li, Zhangjian Zhou PII: DOI: Reference:

S0032-5910(14)00980-2 doi: 10.1016/j.powtec.2014.12.008 PTEC 10669

To appear in:

Powder Technology

Received date: Revised date: Accepted date:

24 June 2014 5 November 2014 5 December 2014

Please cite this article as: Man Wang, Hongying Sun, Lei Zou, Guangming Zhang, Shaofu Li, Zhangjian Zhou, Structural evolution of oxide dispersion strengthened austenitic powders during mechanical alloying and subsequent consolidation, Powder Technology (2014), doi: 10.1016/j.powtec.2014.12.008

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Structural evolution of oxide dispersion strengthened austenitic powders during

T

mechanical alloying and subsequent consolidation

IP

Man Wang1, Hongying Sun2, Lei Zou1, Guangming Zhang1, Shaofu Li1, Zhangjian Zhou1*

SC R

1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 10083, China

NU

2. School of Mechanical Engineering, Anyang Institute of Technology, West of Huanghe Road,

MA

Wenfeng District, Anyang, Henan 455002, China

TE

D

*Corresponding author

Zhangjian Zhou

E-mail address:

[email protected]

AC

Postal address:

CE P

Name:

Laboratory of Special Ceramics and Powder Metallurgy, School of Material

Science and Engineering, University of Science & Technology Beijing, Beijing 100083, P.R.China

Telephone number: +86-10-62334951 Fax number:

+86-10-62334951

1

ACCEPTED MANUSCRIPT

T

Abstract: Different austenitic steel powders with additions of Y2O3 and Ti were fabricated by

IP

mechanical alloying (MA). The structural evolutions during the process of ball milling and

SC R

subsequent annealing were studied by XRD, SEM and TEM. Nano crystalline austenitic powders were obtained by MA. Different ODS austenitic powders presented different phase transition

NU

during the processed of MA and annealing, which were resulted from different contents of Ni and Cr. Both ODS-316 and ODS-310 showed a weak diffraction peak of α after annealing and

MA

consolidated by hot isostatic pressing (HIP) due to the addition of Ti. According to the TEM

D

results, the grain size of all three ODS austenitic steels was around several hundred nanometers.

AC

CE P

TE

Key words: Mechanical alloying; ODS austenitic steels; Phase transition

2

ACCEPTED MANUSCRIPT

1. Introduction

IP

T

Mechanical alloying (MA) was originally developed to produce oxide dispersion

SC R

strengthened (ODS) nickel-base superalloys for application in the aerospace industry. Nowadays MA has shown great potential in fabricating a wide variety of equilibrium and non-equilibrium

NU

alloy phases through high-energy ball milling of blended elemental or pre-alloyed powders [1]. Also, MA has been used to fabricate particle reinforced composite, which can produce uniform

MA

distribution of reinforcement particles in the matrix [2-4]. Recently ODS steels have been investigated widely, since ODS steels are promising candidate materials for generation-Ⅳ

D

advanced reactors [5-9]. The extremely thermally stable oxides can improve the high-temperature

TE

properties of materials. Moreover the interface between oxide particles and matrix is effective sink

CE P

for point defects and helium atoms, resulting in a high irradiation resistance. Recently ODS austenitic steels arouse research interests due to the combination of excellent corrosion resistance

AC

and potential reduced irradiation-induced swelling [10-14]. During the process of MA, great energy and heavy deformation are introduced into the powder particles. At the same time, a high density of crystal defects such as dislocations and grain boundaries are created in the materials. This defective structure can enhance the diffusion of solute elements into matrix, which leads to atomic level alloying and extended solid solution. During the subsequent consolidation, they re-precipitate in the form of complex oxide particle of Y-Ti-O, which plays an important role in improving the high temperature properties of materials [15-17]. It is worth noting that the element of Ti is necessary to the formation of nano scale oxide dispersions [18, 19]. Moreover this process is often accompanied with transformation to metastable phases 3

ACCEPTED MANUSCRIPT with nano-structure. It was found that MA led to the formation of nanostructured BCC and/or FCC phases in Fe-Ni and Fe-Cr-Ni alloys [20-24].

IP

T

It is worth investigating whether the additions of Y2O3 and Ti influence the phase transitions

SC R

of ODS austenitic steels or not. In this work, different types of ODS austenitic steels were fabricated by MA and HIP. The phase transitions and microstructures of ODS austenitic powders

NU

and steels were investigated by XRD and TEM.

MA

2. Experimental

Pre-alloyed 304, 316 and 310 austenitic steel powders were used as the matrix respectively.

D

The designed chemical compositions are shown in Table 1. Ti and Y2O3 were added to form

TE

nano-sized oxide dispersion particles. Fig. 1 shows the SEM morphologies of the original

CE P

materials. The pre-alloyed austenitic steel powders were fabricated by atomization comminuting process. Therefore different austenitic steel powders had a similar morphology, which was round,

AC

as shown in Fig. 1(a). The size and purity of the powders are shown in Table 2. Normally the contents of Y2O3 and Ti for ODS steels are 0.35 wt. % and 0.5 wt. % respectively. To investigate the process of MA, 3 wt. % for both Ti and Y2O3 were used. The starting materials were mechanical alloyed by a planetary high-energy ball mill equipped with stainless jars and milling balls. The milling media were consisted of stainless balls with different sizes and quantities. There were five balls with size of φ20 mm, 400 with size of φ10 mm, and 2000 with size of φ6 mm, which had a total mass of 3608g. Mechanical alloying was conducted at 300 rpm with a ball-to-powder mass ratio of 5:1 under nitrogen atmosphere. Samples were taken at different milling time intervals. Isothermal annealing was carried out at 700, 900 and 4

ACCEPTED MANUSCRIPT 1200 ℃ for 1h in a muffle furnace. The mechanical alloyed powders were consolidated by hot isostatic pressing (HIP) under a pressure of 100 MPa. The process of HIP consisted of two stages:

IP

T

first at 1100 ℃ for 2 h and then at 1150 ℃ for 1 h.

SC R

The morphology of powders before and after mechanical alloying was investigated by Scanning Electron Microscope (SEM, LEO-1450). The structural changes were characterized by X-Ray diffraction using filtered Cu Kα radiation (λ=0.15406 nm). The crystalline size of phases

NU

was obtained by using Hall-Williamson method. A standard sample of silicon was used for

MA

correcting the instrumental broadening. The phase fractions of austenite and martensite were estimated according to their diffraction intensity. The microstructure of the block samples was

D

investigated by Transmission Electron Microscopy (TEM, JEM 2010). Foil samples for TEM were

TE

prepared through jet-polishing at -30 ℃ by using 15% perchloric acid and 85% methanol as the

CE P

electrolyte. The Vickers hardness of powder particles was determined by a micro-hardness tester (MH-6) at a load of 100 g and dwell time of 15 s.

AC

3. Results and discussion

3.1 Structural evolution of ODS powders during ball milling

Fig. 2 shows the SEM images of ODS-310 powders at different time intervals. As shown in Fig. 2(a), the powders became flat after milling of 5 h due to the collisions between balls, powders and jar. The average diameter of the powders was about 100 μm. After milling of 30 h, the disk-type particles became round and the size increased to 200 μm resulted from cold welding, as shown in Fig. 2(b). The particles became fragmented after milling of 50 h and most of them decreased to 20 μm (Fig. 2(c)). During the process of MA, accumulated strain and work hardening 5

ACCEPTED MANUSCRIPT led to severe brittleness and therefore the size became smaller. It is worth noting that ODS-304 powders showed similar changes in both morphology and size during the process of MA.

IP

T

Fig. 3 and Fig. 4 are the XRD patterns of ODS-304 and ODS-310 powders respectively

SC R

during the process of MA. We can see that the diffraction peaks of Y2O3 and Ti vanished for both of them after milling of 5 h. Also the main diffraction peaks displaced towards the smaller angel, which indicated that the additions of Y2O3 and Ti were dissolved into the matrix. Moreover, all the

NU

diffraction peaks became broader with increasing milling time due to grain refinement and

MA

accumulated strain.

Fig. 5 shows the changes of grain size during the process of milling. After milling of 5 h, the

D

grain size of both ODS-304 and ODS-310 powders decreased to 18.9 nm, although their phase

TE

component was different. The grain size decreased further to 12.8 nm and 9.4 nm after milling of

CE P

50 h respectively, which indicated that both of them achieved nano-crystalline structure after ball milling. From Fig. 6 we can see that both of them showed an increasing trend in micro-hardness

AC

with increasing milling time. For ODS-304 powders, the micro-hardness increased from 391 Hv to 587 Hv, while the micro-hardness of ODS-310 powders increased from 378 Hv to 556 Hv. ODS-304 and ODS-310 powders showed similar changing trends in grain size and micro-hardness, as well as mechanical alloying. However, their phase transitions were different during the process of ball milling. As shown in Fig. 3, the starting powders of ODS-304 had a dual-phase structure consisting of γ and α, in which the fraction of γ was higher than α according to the diffraction intensity. However, the γ phase completely transformed into α after milling of 5 h. On the contrary, ODS-310 powders stayed γ even after milling of 50 h (Fig. 4). This indicated that ODS-310 powders had greater austenite stability due to relatively higher content of Ni, since 6

ACCEPTED MANUSCRIPT Ni is a notable austenite forming element.

T

3.2 Structural evolution of ODS powder during annealing

IP

Fig. 7 shows the XRD patterns of ODS-304 powders after annealing at different temperatures.

SC R

We can see that the single-phase milled powders transformed into two phases of γ and α. With higher annealing temperature, the fraction of γ increased and the fraction of α decreased, as shown

NU

in Fig. 8. The strain was eliminated during annealing, therefore α transformed back to γ. Also the

MA

grain size of both γ and α increased after annealing, and the phase of γ had a relatively larger average grain size, which was 54.7 nm, as shown in Fig. 9. After annealing at 700 ℃ for 1 h, the

D

micro-hardness of the as-milled ODS-304 powders decreased from 587 Hv to 394 Hv. As shown

TE

in Fig. 10, there were no obvious differences among different annealing temperatures. Compared

CE P

with the as-milled powders, the as-annealed powders showed larger standard deviation in micro-hardness (Fig. 6 and Fig. 10), which was related to the dual-phase structure. Fig. 11 shows the XRD patterns of ODS-310 powders after annealing at different

AC

temperatures. It can be seen that γ was the predominant phase in all cases. However, there are some precipitates of Cr0.99Fe1.01 at 700 and 900 ℃. After annealing at 1200 ℃ for 1 h, these precipitates disappeared and the phase of α occurred, but its diffraction peaks were relatively weak. During the process of MA, a high density of defects are created, which makes material transfer by diffusion much easier and achieve atomic level alloying [25]. In this case, 3 wt. % of Y2O3 and Ti were added. The added powders of Y2O3 and Ti dissolved into the matrix in the form of atoms during the process of MA. They re-precipitated during annealing. ODS-310 powders

7

ACCEPTED MANUSCRIPT stayed austenite even after milling of 50 h, which was resulted from higher content of Ni. However, diffraction peaks of α occurred after annealing at 1200 ℃. This may be influenced by

SC R

phase transition since it is a notable ferrite forming element.

IP

T

the element of Ti. Ti existed in the form of atom after MA, and during annealing it influenced the

Fig. 12 shows the micro-hardness of ODS-310 powders during annealing. The micro-hardness of the as-milled ODS-310 powders decreased from 556 Hv to 391 Hv after

NU

annealing at 700 ℃. There was no obvious difference between 900 and 1200 ℃, both of which

MA

were around 260 Hv. The grain size of ODS-310 powders showed an increasing trend with higher annealing temperatures, as shown in Fig. 13. After annealing at 1200 ℃, the grain size increased

TE

D

to 54.7 nm.

CE P

3.3 Phase transitions of ODS austenitic powders

The phase transitions of as-milled ODS austenitic powders and as-Hipped ODS austenitic

AC

steels are shown in Fig. 14, Fig. 15 and Fig. 16. It is worth noting that normal contents of Y2O3 (0.35 wt. %) and Ti (0.5 wt. %) were used for these as-milled powders and as-Hipped blocks. It is very interesting that the phase transitions were different depending on different austenitic matrixes, namely different contents of Ni and Cr. Ni is a notable austenite forming element and Cr is a ferrite forming element, therefore they decide the phase transition together. The as-milled ODS-304 powders were single phase of α, while the as-milled ODS-310 powders were single phase of γ. Both of them were the same with cases where 3 wt.% of Y2O3 and Ti were used (Fig. 3 and Fig. 4). In contrast to ODS-304 and ODS-310 powders, the as-milled ODS-316 had a dual phase structure consisting of α and γ. This is because higher content of Ni has greater austenite

8

ACCEPTED MANUSCRIPT stability and greater resistance of strain-induced transformation. These results were the same with the phase transitions of traditional Fe-Cr-Ni alloys during ball milling [20-24].

IP

T

After consolidated by HIP, different ODS austenitic steels showed different structures.

SC R

ODS-304 had a dual phase structure, of which γ was the predominant phase. ODS-316 and ODS-310 were single phase of γ. Moreover, both of them showed a very weak diffraction peak of α, as shown in Fig. 15 and Fig. 16. As discussed in Part 3.2, ODS-310 powders with higher

NU

content of Ti (3 wt.%) had a relatively obvious diffraction peak of α after annealing at 1200 ℃.

MA

This is different from the phase transitions of traditional Fe-Cr-Ni during annealing [20-24]. For the traditional Fe-Cr-Ni, if the matrix stayed austenite during ball milling, there would be no phase

D

transition during annealing. Therefore the addition of Ti may influence the phase transition of γ to

TE

α during annealing or consolidation, and the higher content of Ti makes the transition easier. Since

CE P

Ti is necessary for the formation of nano scale oxide dispersions[18, 19], special attention should be paid to the content of Ti when ODS austenitic steels are fabricated.

AC

3.4 Microstructure of as-hipped ODS austenitic steels The mechanically alloyed powders were consolidated by HIP first at 1100 ℃ and then at 1500 ℃ totally for 3 h. The microstructures of as-hipped ODS austenitic steels are shown in Fig. 17. From Fig. 17 (a)-(c), we can see that the grain size of these three ODS steels was around a few hundred nanometers. The corresponding images at a larger amplification were shown in Fig.17 (d)-(f), which showed that nano-sized particles were distributed inside grains. We have investigated these nano particles in other works [13, 14], and they were characterized to be enriched in Y-Ti-O, which played an important role in ODS alloys. Among these three ODS steels,

9

ACCEPTED MANUSCRIPT ODS-316 exhibited a relatively larger grain size, which was around 300 nm, while the grain size of ODS-310 was around 150 nm. It should be noted that the distribution of grains was not very

IP

T

uniform, but most of them are around several hundred nanometers. From Fig. 17(d) to (f), we can

SC R

see that the distributions of nano-sized particles in ODS-304 and ODS-310 were more uniform and dense that those in ODS-316. This can be contributed to the different grain sizes of ODS

NU

steels.

MA

4. Conclusions

In this paper, we investigated the structural evolutions of ODS austenitic powders during the

TE

D

process of ball milling and annealing. Also the phase transition and microstructures of as-Hipped

research.

CE P

ODS austenitic steels were studied. The following results can be obtained according to our

(1) Different ODS austenitic powders showed different austenite stability which was related

AC

to the contents of Ni and Cr. ODS-304 powders completely transformed into α after ball milling; ODS-316 powders had a dual phase of γ and α, while ODS-310 powders stayed austenite even after milling of 50 h. (2) A weak diffraction peak of α was found in both the as-Hipped ODS-316 and ODS-310, which indicates that the addition of Ti may influence the phase transition of ODS austenitic steels. This should be considered carefully when ODS austenitic steel are fabricated. (3) According to the XRD results, both the mechanically alloyed powders and the annealed powders had nano-scaled grain size. This was confirmed by the TEM observation of as-hipped ODS samples. The grain sizes of all three ODS austenitic steels were around a few hundred 10

ACCEPTED MANUSCRIPT nanometers.

IP

T

Acknowledgements

SC R

The authors would like to express their thanks for the financial support of National Basic Research Program of China under Grant No. 2007CB209801, and also thanks for the support of

NU

IAEA Coordinated Research Project (CRP code:T11006) under research contract No. 16763.

MA

References

D

[1] C. Suryanarayana, Mechanical alloying and milling, Progress in Material Science, 46 (2001)

TE

1-184.

CE P

[2] T. Varol, A. Canakci, Synthesis and characterization of nanocrystalline Al 2024-B4C composite powders by mechanical alloying, Philosophical Magazine Letters, 93 (2013) 339-345.

AC

[3] T. Varol, A. Canakci, Effect of particle size and ratio of B4C reinforcement on properties and morphology of nanocrystalline Al2024-B4C composite powders, Powder Technology, 246 (2013) 462-472. [4] A. Canakci, T. Varol, H. Cuvalci, F. Erdemir, S. Ozkaya, E.D. Yalcin, Synthesis of novel CuSn10-graphite nanocomposite powders by mechanical alloying, Micro & Nano Letters, 9 (2014) 109-112. [5] C. Suryanarayana, E. Ivanov, V. V. Boldyrev, The science and technology of mechanical alloying, Materials Science and Engineering A 304-306 (2001) 151-158. [6] M. K. Miller, E. A. Kenik, K. F. Russell, L. Heatherly, D. T. Hoelzer, P. J. Maziasz, Atom 11

ACCEPTED MANUSCRIPT probe tomography of nanoscale particles in ODS ferritic alloys, Materials Science and Engineering A 353 (2003) 140-145.

SC R

Journal of Nuclear Materials 307-311 (2002) 749-757.

IP

T

[7] S. Ukai, M. Fujiwara, Perspective of ODS alloys application in nuclear environments,

[8] R .L. Klueh, A. T. Nelson, Ferritic/martensitic steels for next-generation reactors, Journal of Nuclear Materials 371 (2007) 37-52.

NU

[9] K. L. Murty, I. Charit, Structural materials for Gen-Ⅳ nuclear reactors: Challenges and

MA

opportunities, Journal of Nuclear Materials 383 (2008) 189-195. [10] T. Ky. Kim, Ch. S. Bae, D. Hy. Kim, J. S. Jang, S. H. Kim, Ch. B. Lee, D. Hahn,

D

Micro-structural observation and tensile isotropy of an austenitic steel, Nuclear Engineering

TE

and Technology 40 (2008) 305-310.

CE P

[11] Y. L. Xu, Zh. J. Zhou, M. Li, P. He, Fabrication and characterization of ODS austenitic steels, Journal of Nuclear Materials 417 (2011) 283-285.

AC

[12] H. Oka, M. Watanabe, H. Kinoshita, T. Shibayama, N. Hashimoto, S. Ohnuki, S. Yamashita, S. Ohtsuka, In situ observation of damage structure in ODS austenitic steel during electron irradiation, Journal of Nuclear Materials 417 (2011) 279-282. [13] M. Wang, Zh. J. Zhou, H. Y. Sun, H. L. Hu, Sh. F. Li, Effects of plastic deformations on microstructure and mechanical properties of ODS-310 austenitic steels, Journal of Nuclear Materials 430 (2012) 259-263. [14] M. Wang, Zh. J. Zhou, H. Y. Sun, H. L. Hu, Sh. F. Li, Microstructural observation and tensile properties of ODS-304 austenitic steels, Materials Science and Engineering A 559 (2013) 287-292. 12

ACCEPTED MANUSCRIPT [15] M. K. Miller, E. A. Kenik, K. F. Russell, L. Heatherly, D. T. Hoelzer, P. J. Maziasz, Atom probe tomography of nanoscale particles in ODS ferritic alloys, Materials Science and

IP

T

Engineering A 353 (2003) 140-145.

SC R

[16] H. Kishimoto, M. J. Alinger, G. R. Odette, T. Yamamoto, TEM examination of microstructural evolution during processing of 14CrYWTi nanostructured ferritic alloys, Journal of Nuclear Materials 329-333 (2004) 369-371.

NU

[17] L. Dai, Y. Ch. Liu, Zh. Zh. Dong, Size and structure of yttria in ODS ferritic alloy powder

MA

during mechanical milling and subsequent annealing, Powder Technology 217 (2012) 281-287.

D

[18] M. J. Alinger, G. B. Odette, D. T. Hoelzer, The development and stability of Y-Ti-O

TE

nanoclusters in mechanically alloyed Fe-Cr based ferritic alloys, Journal of Nuclear Materials

CE P

329-333 (2004) 382-386.

[19] R. Kasada, N. Toda, K. Yutani, H.S. Cho, H. Kishimoto, A. Kimura, Pre- and

AC

post-deformation microstructures of oxide dispersion strengthened ferritic steels, Journal of Nuclear Materials, 367-370 (2007) 222-228. [20] X. F. Fang, W. Dahl, Strain hardening and transformation mechanism of deformation induced martensite transformation in metastable austenitic stainless steels, Materials Science and Engineering A 141 (1991) 189-198. [21] H. Huang, J. Ding, P.G. McCormick, Microstructural evolution of 304 stainless steel during mechanical milling, Materials Science and Engineering A 216 (1996) 178-184. [22] V. V. Tcherdyntsev, S. D. Kaloshkin, I. A. Tomilin, E. V. Shelekhov, Yu. V. Baldokhin, Formation of iron-nickel nanocrystalline alloy by mechanical alloying, NanoStructed 13

ACCEPTED MANUSCRIPT Materials 12 (1999) 139-142. [23] D. Oleszak, A. Grabias, M. Pekala, A. Świderska-Środa, T. Kulik, Evolution of structure in

IP

T

austenitic steel powders during ball milling and subsequent sintering, Journal of Alloys and

SC R

Compounds 434-435 (2007) 340-343.

[24] M. H. Enayati, M. R. Bafandeh, S. Nosohian, Ball milling of stainless steel scrap chips to produce nanocrystalline powder, Journal of Materials Science 42 (2007) 2844-2848.

NU

[25] M. H. Enayati, M. R. Bafandeh, Phase transitions in nanostructured Fe-Cr-Ni alloys prepared

AC

CE P

TE

D

MA

by mechanical alloying, Journal of Alloys and Compounds 454 (2008) 228-232.

14

ACCEPTED MANUSCRIPT

T

Table Captions

AC

CE P

TE

D

MA

NU

Table 2 Particle size and purity of the starting powders

SC R

IP

Table 1 The designed chemical compositions of austenitic steel powders (wt. %)

15

ACCEPTED MANUSCRIPT

T

Figure Captions

SC R

IP

Fig. 1 SEM morphologies of the original materials

NU

Fig. 2 SEM images of ODS-310 powders (a) 5 h (b) 30 h (c) 50 h

MA

Fig. 3 XRD patterns of ODS-304 powders at different milling intervals

TE

D

Fig. 4 XRD patterns of ODS-310 powders at different milling intervals

CE P

Fig. 5 Grain size of ODS austenitic powders at different milling intervals

AC

Fig. 6 Micro-hardness of ODS austenitic powders at different milling intervals

Fig. 7 XRD patterns of ODS-304 powders after annealing at different temperatures

Fig. 8 Phase fractions of ODS-304 powders after annealing at different temperatures

Fig. 9 Grain size of ODS-304 powders as a function of annealing temperature

Fig. 10 Micro-hardness of ODS-304 powders after annealing at different temperatures

16

ACCEPTED MANUSCRIPT Fig. 11 XRD patterns of ODS-310 powders after annealing at different temperatures

Fig. 13 XRD patterns of ODS-316 powders and block

MA

NU

Fig. 14 XRD patterns of ODS-310 powders and block

SC R

IP

T

Fig. 12 XRD patterns of ODS-304 powders and block

D

Fig. 15 XRD patterns of ODS-316 powders and block

CE P

TE

Fig. 16 XRD patterns of ODS-310 powders and block

AC

Fig. 17 TEM images of as-hipped ODS austenitic steels

17

Fig. 1 (a)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 1 SEM morphologies of the original materials

AC

CE P

TE

D

MA

(a) pre-alloyed 316 powders (b) Ti powder (c) Y2O3 powder

18

Fig. 1(b)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 1 SEM morphologies of the original materials

AC

CE P

TE

D

MA

(a) pre-alloyed 316 powders (b) Ti powder (c) Y2O3 powder

19

Fig. 1 (c)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 1 SEM morphologies of the original materials

AC

CE P

TE

D

MA

(a) pre-alloyed 316 powders (b) Ti powder (c) Y2O3 powder

20

Fig. 2(a)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 2 SEM images of ODS-310 powders

AC

CE P

TE

D

MA

(a) 5 h (b) 30 h (c) 50 h

21

Fig. 2(b)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 2 SEM images of ODS-310 powders

AC

CE P

TE

D

MA

(a) 5 h (b) 30 h (c) 50 h

22

Fig. 2(c)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 2 SEM images of ODS-310 powders

AC

CE P

TE

D

MA

(a) 5 h (b) 30 h (c) 50 h

23

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 3 XRD patterns of ODS-304 powders at different milling intervals

24

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 4 XRD patterns of ODS-310 powders at different milling intervals

25

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 5 Grain size of ODS austenitic powders at different milling intervals

26

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 6 Micro-hardness of ODS austenitic powders at different milling intervals

27

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 7 XRD patterns of ODS-304 powders after annealing at different temperatures

28

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 8 Phase fractions of ODS-304 powders after annealing at different temperatures

29

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 9 Grain size of ODS-304 powders as a function of annealing temperature

30

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 10 Micro-hardness of ODS-304 powders after annealing at different temperatures

31

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 11 XRD patterns of ODS-310 powders after annealing at different temperatures

32

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 12 Micro-hardness of ODS-310 powders after annealing at different temperatures

33

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 13 Grain size of ODS-310 powders after annealing at different temperatures

34

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 14 XRD patterns of ODS-304 powders and block

35

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 15 XRD patterns of ODS-316 powders and block

36

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 16 XRD patterns of ODS-310 powders and block

37

Fig. 17(a)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

38

Fig. 17(b)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

39

Fig. 17(c)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

40

Fig. 17(d)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

41

Fig. 17(e)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

42

Fig. 17(f)

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

Fig. 17 TEM images of as-hipped ODS austenitic steels

AC

CE P

TE

D

MA

(a), (d) ODS-304; (b), (e) ODS-316; (c), (f) ODS-310

43

ACCEPTED MANUSCRIPT Table 1 The designed chemical compositions of austenitic steel powders (wt. %) Fe

Cr

Ni

Mo

Pre-alloyed 304

Bal.

18

8

1

Pre-alloyed 316

Bal.

16

12

2

Pre-alloyed 310

Bal.

25

20

-

AC

CE P

TE

D

MA

NU

SC R

IP

T

kinds of powder

44

ACCEPTED MANUSCRIPT Table 2 Particle size and purity of the starting powders purity

size

Pre-alloyed 304 Pre-alloyed 316 Pre-alloyed 310 Ti Y2O3

99.9% 99.9% 99.9% 99.7% 99.99%

150 μm 48 μm 150 μm 48 μm 30 nm

AC

CE P

TE

D

MA

NU

SC R

IP

T

kinds of powder

45

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

Graphical abstract

46

ACCEPTED MANUSCRIPT Highlights  Different ODS austenitic powders showed different phase transitions during MA.

T

Nano-structural ODS austenitc powders were obtained by MA. The average grain size of

IP

as-hipped samples was around several hundred nanometers.

SC R

ODS-304 and ODS-316 austenitic powders completely transformed into α after MA, while ODS-310 stayed γ.

NU

The element of Ti favored the transformation of γ to α in ODS austenitic powders during

AC

CE P

TE

D

MA

annealing and consolidation

47