Stability of Colossally Supersaturated Alloys

Lead Research Organisation: University of Birmingham
Department Name: Metallurgy and Materials

Abstract

The work our groups have carried out on alloys exposed to recently developed processes for low-temperature carburising and nitriding revealed that extraordinarily high concentrations of carbon and nitrogen can be dissolved in Fe-Cr-Ni alloys (austenitic stainless steel). In this process, carbon or nitrogen diffuses into the alloy from the surface at a temperature sufficiently low to suppress the precipitation of carbides or nitrides. This enables the formation of a homogeneous, precipitate-free, superhard " S-phase" consisting with carbon or nitrogen concentrations that exceed the equilibrium solubility limit by about one-hundred-thousand times!

To date, our work has focused on the underlying physical principles of this "colossal supersaturation" (CSS) and the mechanical properties and corrosion resistance of the as-processed 25-50 micron -thick hardened layer provided by the interstitial solute ("case") below the surface. The work we propose here constitutes a first effort to investigate the reliability and lifetime of this unusual material at elevated temperature and under applied mechanical stress and to further process it by tempering - i. e. exposure to heat treatments. Moreover, we propose to extend the research to Ni-Cr and Co-Cr alloys, for which hardening by colossal supersaturation has great technological importance.

Alloys with a colossal supersaturation of interstitial solute (carbon, nitrogen) constitute unique model systems for fundamental studies of decomposition and precipitation phenomena in metals under unusual conditions. In particular, it will enable understanding the physical principles of carbide and nitride nucleation, growth, and ripening under extremely high supersaturation and how the decomposition affects the remarkable mechanical properties and outstanding corrosion resistance initially provided by CSS. This provides a high potential for "transformative" discoveries. The largely complementary expertise, experience, and instrumentation of the two involved research group will enable significant progress in this important field of surface engineering.

This project will lay the foundation for long-term cooperation of two leading groups in the field of surface engineering. The physical understanding of the decomposition of CSS-hardened alloys under applied temperature and stress we intend to obtain is of great importance for many applications of structural alloys, e. g. bearings, food processing blades, valves, bushings, dies, nuclear reactor components, medical implants and surgical and dental instruments. The increase of reliability and lifetime we hope to enable by understanding their physical foundations will lead to major savings of primary energy resources and conservation of strategic raw materials by avoiding unnecessary production and recycling of alloy parts. The availability of super-hard wear-and corrosion-resistant alloys will strengthen US and UK industry by enabling the design of new products, which can contribute to the creation of new jobs. The long-life body implants can improve the quality of life of patients and reduce UK/US health service costs. The results of the proposed research are highly likely to generate new intellectual property.

The project will have significant impact on student education and training at CWRU and UoB. The results will directly impact the theoretical and practical parts of materials science courses at both universities. Further, the project will enable significant practical participation of undergraduate students and will therefore help to attract excellent undergraduate students to our institutions. The PIs have a record in engaging undergraduate students and women students and in exchanging research students and postdoctoral research associates in their research activities.

Planned Impact

The proposed collaborative research will systematically investigate the stability of S-phase formed in para-equilibrium hardened corrosion-resistant alloys under thermal (temperature), mechanical (stress) and both thermal and mechanical conditions via both theoretical and experimental approaches, thus advancing scientific understanding of S-phase and facilitating the safe use of the S-phase surface engineering technology. The impacts forecasted from the project are four-fold:

(1) Scientific impact - The materials research community
This US/UK collaborative research is expected to produce significant scientific impacts mainly through greatly advancing scientific understanding of the metastability of S-phase, which will significantly enrich materials science knowledge and physical metallurgy and surface engineering in particular. Other researchers will benefit from better understanding of the metastability of S-phase through developing new alloys and/or new para-equilibrium hardening processes to generate more stable S-phase. PhD students and post-doctorial research fellows will benefit from being engaged in world-leading S-phase research.

(2) Technological benefits - Engineering component and medical device designers
The stability maps and modelling tools developed from this research can provide engineering components and medical device designers with essential tools for the design and manufacture of reliable, high-performance and long-life engineering components (such as for nuclear reactors, for the chemical and petrochemical processing and for food equipment) as well as medical devices (such as joint prostheses and bone fixation devices).

(3) Economic benefits - UK P.L.C. & NHS
UK surface engineering and many other many industrial sectors (especially the nuclear reactor, chemical, petrochemical and food equipment, and medical device sectors) will benefit from the reliable S-phase treated components with high performance and prolonged life-span through developing product market, enhancing global competitiveness and increasing wealth creation. The NHS will also benefit greatly from high performance, long-life medical devices (cost-saving).

(4) Societal & ecological impact - Aging population and everyone
The aging population will benefit most from the provision of joint replacements with improved durability and reduced risk of corrosion-induced premature failure of S-phase surface engineered joints prostheses. Equally, reliable surface treated components for nuclear reactors and for chemical and petrochemical processing equipment can avoid potential life and environment disaster. In addition, prolonged life of corrosion resistant components can reduce the consumption of strategic elements (such as Cr and Ni) and energy.

Publications

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Dong Y (2015) Towards near-permanent CoCrMo prosthesis surface by combining micro-texturing and low temperature plasma carburising. in Journal of the mechanical behavior of biomedical materials

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Li X (2013) Low temperature plasma surface alloying and characterisation of a superduplex stainless steel in International Heat Treatment and Surface Engineering

 
Description Tensile stress reduces the stability of S-phase
Compressive stress increases the stability of S-phase
It is possible to further increase the hardness of S-phase by rapid heating and cooling
Exploitation Route Publication research output; further INNOVATE project applications with industry partners
Sectors Agriculture, Food and Drink,Chemicals,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Security and Diplomacy,Transport

 
Description The findings have been used as a guide ling for the industry application of the S-phase layer formed on the austenitic stainless steel.
First Year Of Impact 2017
Sector Agriculture, Food and Drink,Chemicals,Energy
Impact Types Societal,Economic,Policy & public services

 
Description An industry system enabling the use of a patented materials processing technology for Low Cost forming of Lightweight structures for transportation industries (LoCoLite)
Amount € 542,480 (EUR)
Funding ID 604240 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 12/2013 
End 11/2016
 
Description Modified cost effective fibre based structures with improved multi-functionality and performance MODCOMP
Amount € 716,067 (EUR)
Funding ID GA685844 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 04/2016 
End 03/2020
 
Description PhD studentship
Amount £3,120,000 (GBP)
Funding ID EP/L016206/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 09/2014 
End 09/2022
 
Description Stability of S-phase under thermal and radiation conditions
Amount £12,000 (GBP)
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 03/2016 
End 02/2018
 
Title Double-glow plasma (DGP) alloying 
Description Double-glow plasma (DGP) alloying technique was developed to produce a relatively thick (up to ~100 µm) alloyed layer at a certain temperature which was decided by the phase diagram of the alloying elements and the matrix. A typical GDP unit consists of two cathodes: parts cathode - and source cathode (metal) with the wall as the anode. When the two power supplies are turned on, a negative potential is applied to the source and the parts in a vacuum chamber containing a low pressure of inert gas such as Argon. Both the parts and metal source are bombarded by ions (such as Ar+) and glow discharge forms on the both cathodes (hence the name 'double glow'). Under the bombardment of energetic ions, both the source cathode and the parts cathode are heated up and metal is sputtered out from the source due to a higher voltage supplied on it. These sputtered metal ions and atoms move towards the parts and then diffuse into the parts to form an alloying layer with novel multi-functional surfaces. 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? Yes  
Impact By combining the ASPN technique and double-glow plasma (DGP) alloying technique, two kinds of new hybrid plasm facilities with samples floated or biased were designed and installed; A duplex layer composed of a thin Ag containing deposition layer (less than 500nm) and an S-phase diffusion layer was formed using these two kinds of facilities at working pressure of 4mbar; A deposition layer with thickness more than 2µm formed on the nitriding diffusion layer when the working was reduced to 1mbar; Higher Ag-N co-alloying temperature (450?) could result in a thick deposition and diffusion layer formed on the 316 ASS. However, it induced a poor corrosion resistance than 316 ASS due to chromium precipitation along the grain boundary; The Ag-N co-alloyed layer prepared at a lower temperature of 420? and sample bias of 240V was composed of a compact Ag doped S-phase deposition layer and S-phase diffusion layer. It indicted a combining of high hardness and better corrosion resistance than 316 ASS; It did not show obviously changing for the Ag content in the deposition layer by changing the distance between the Ag plate and SS lid; The Ag-N co-alloyed layer prepared at temperature of 420-430?, sample bias of 240V-280V, and working pressure of 1-1.5mbar can supply multi-functional properties for the ASS which was a combination of high hardness, good adhesion, excellent wear resistance, similar corrosion resistance to 316 ASS in the Ringers solution and high anti-bacterial efficacy. 
 
Description Collabration with Prof Tschiptschin of University of San Paulo supported by FAPESP/UoB 
Organisation University of Sao Paulo
Department Metallurgical and Materials Engineering Department
Country Brazil 
Sector Academic/University 
PI Contribution The Birmingham group has done systematic work on S-phase including: active-screen plasma S-phase surface engineering, S-phase surface engineering of duplex and precipitation stainless steels, duplex surface engineering involving S-phase, erosion-corrosion & corrosion-wear, mechanical and/or thermal stability of S-phase. The objectives of the project focus on oil and gas aiming at a) minimizing the erosive-corrosive wear of metal parts in contact with oil/sea-water/sand, containing high concentrations of chloride and particulate silica and b) minimizing the risk of catastrophic accidents due to hydrogen embrittlement of pipelines in contact with oil/sea water /sand, containing a high concentration of H2S and CO2.
Collaborator Contribution The research work carried out by the Brazilian group focuses on S-phase formation and duplex treatment of austenitic, martensitic and duplex stainless steels and the benefits that S-phase can bring to the improvement of erosion-corrosion, cavitation-erosion and hydrogen embrittlement of stainless steel valves and parts to be used at high depths in the pre-salt exploitation wells.
Impact A few papers
Start Year 2013
 
Description Stability of S-phase under thermal and radiation conditions 
Organisation Sichuan University
Country China 
Sector Academic/University 
PI Contribution UoB team to produce S-phase by plasma treatment and the stability of S-phase in radiation conditions and radiation damage mechanism of S-phase will be evaluated by proton irradiation .
Collaborator Contribution SU team produce S-phase by liquid treatment and the stability of S-phase will be tested in high-temperature, high pressure water using autoclave.
Impact 1. Seminars held in Sichun University on the project topics in 2016 and 2017
Start Year 2016
 
Description PhD student exchange, Qiong 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact QIong Li worked in our group for three months and carried out the project related research work. She gave two talks on her research work related to the project: the work she did in her own university, Case Western Reserve University, and the work she did in our lab. This activity exchanged the research expertise of two world leading groups on the surface plasma treatments of austenitic stainless steels and a further collaborative research plan for the project was made.
Year(s) Of Engagement Activity 2014
 
Description PhD student exchange, Dennis 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Dennis worked in Surface Engineering group of Case Western Reserve University, USA for three months and carried out the project related research work there. He was participated in their group activities and received trainings on varies microstructure analysis techniques. This activity exchanged the research expertise of two world leading groups on the researches of surface treatments of austenitic stainless steels and a further collaborative research plan for the project was made.
Year(s) Of Engagement Activity 2014,2015
 
Description School visit in Case Western Reserve University, Hanshan 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Prof Hanshan Dong visited the project partner, Case Western Reserve University, USA and gave a seminar talk in Department of Materials Science and Engineering. About 100 people attended the seminar and followed by an active discussion. Several individual meetings booked afterwards for possible collaboration discussion
Year(s) Of Engagement Activity 2013
 
Description Visit Case Western Reserve University and give a talk, Moataz 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact A team of four members from Birmingham University visited project partner in Case Western Reserve University for project discussion. At the same time, Prof M Attallah was invited to give a talk on Microstructural Characteristics of Direct Laser Fabrication (DLF) products in Al, Ni, and Ti alloys. The talk was attracted about 100 people from the region and afterwards discussions were very active. One of the audience invited Prof M Attallah for an extra talk the day after in a peer professional institute.
Year(s) Of Engagement Activity 2014
 
Description Visit of Professor Frank Ernst to University of Birmingham 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact About 50 colleagues and students attended this research project related talk. Questions and discussions were very active afterwards and a few academics made individual discussions with the speaker after the talk.

A carbon diffusion in steel mode was discussed between the talker and Dr Martin Strangwood and some suggestions were made.
Year(s) Of Engagement Activity 2013