Elsevier

Calphad

Volume 61, June 2018, Pages 219-226
Calphad

Invited paper: Kinetic diffusion multiple: A high-throughput approach to screening the composition-microstructure-micromechanical properties relationships

https://doi.org/10.1016/j.calphad.2018.04.001Get rights and content

Abstract

We introduced a strategic "Kinetic Diffusion Multiple" (KDM) that undergoes interdiffusion annealing followed by realistic thermal treatment. The blended spectra of phases and microstructures subjected to treatment in deeply grooved composition gradients enables the microstructure and micromechanical properties of structural materials to be surveyed by high-spatially resolved micro-analysis along the composition arrays. The KDM was demonstrated as a robust high-throughput methodology that enables rapid screening of the composition-microstructure-micromechanical/properties relationships for different metallic materials. It has also proven great success at elucidating the lasting effects of alloying elements and diffusion flux on microstructure, micromechanical properties, phase transformation, and their interrelationships as a whole.

Introduction

The discovery, development, and optimization of today's new materials are facing three interrelated challenges [1], namely, advanced materials are often i) highly tailored, ii) formulated from multicomponents, and iii) exhibit intrinsic structure and behavior, thereby creating huge complex variable spaces to be explored. In years past, materials design significantly relied on a huge number of experiments for design, processing, and testing, largely by trial and error. Nowadays, the advances in computer science and modern characterization tools provoke knowledge-based materials design, which is placing unprecedented demands on the link between the associated variable space of target materials including composition, processing, microstructure and resultant mechanical properties.

In recent years, high throughput techniques have boosted acquiring the composition-microstructure link of materials for example by diffusion couple [2], [3], [4], [5], [6] as well as mapping the materials composition-properties link. Regarding the latter, a variety of experimental high throughput approaches have been developed that permit screening of the composition-property link in order to generate combinatorial libraries for a broad range of materials [7], [8], [9] such as thin film systems, functional materials such as shape memory alloys [10] and magnetic materials [11], and structural polymers [12]. As for bulk systems, the diffusion multiple approach, extended from the diffusion couple [13] and diffusion triple [14], [15] techniques in metallurgy research, has been put forward to create the composition-property library (so far focused on thermo-physical properties including heat capacity, thermal conductivity and elastic constant, etc.), along with compositional phase diagram data, of ternary and multicomponent bulk metallic materials in a phase-based perspective [16], [17].

Nevertheless, it is quite well known that in structural materials, not only by chemical composition, the mechanical behavior is to a large extent governed also by their microstructural attributes such as phase present and distribution and grain size at the scale of several nanometers and multiple micrometers, which define the microstructure-properties link. This microstructure-property link is essentially recognized as an indicator of heat/mechanical treatments, which consists of casting, heat/mechanical treatment and forming etc., conventionally applied by sequential fabrication/processing of homogeneous bulk specimens. This sequential complexity gives rise to difficulty in preparing high throughput bulk combinatorial samples of structural materials, thereby leaving conventional alloy discovery and development largely one alloy at a time.

Nowadays, in view of the fact most of bulk (structural) materials are often both profoundly sensitive to chemistry and processing, there is a strong demand to delineate a full composition-microstructure-property link as both composition and microstructure are required to derive the resulting properties/performance. High throughput experimental technique is well suited to the task. This is particularly due to technical difficulties for any one-alloy-a-time approach (e.g. traditional equilibrated alloy method) in which requires obtaining realistic compositional homogeneity of target bulk materials and finding its genuine microstructure in response to the applied processing. This complicates determination of the outcomes from different experimental runs as functions of both compositions and microstructures, because associated effecting factors are difficult and/or costly to control. Innovative high throughput work to tackle these difficulties include: Gallant et al., via introducing thermo-mechanical gradients and surveying the processing parameters that influence bulk energy materials [18], in situ screening that acquired the evolution of phases associated with gas-solid reactions in combinatorial catalyst libraries [19], and the process-property linkage of structural Al-6061 alloy [20].

Meanwhile, promising high throughput diffusion studies have focused on materials subjected to either diffusion annealing or processing by a single stage that essentially generates a single array, either continuous or discrete, of compositions or processing of materials without further treatments, thus rendering it a one-array-at-a-time approach. New advance in bulk materials were suggested to envisage freezing the spinodal decomposition of a hypothetical binary system [21], to scan the mechanical properties versus nine ageing treatments over 5 semi-continuously processed triplex steels with varied compositions [22], and to investigate phase diagrams and massive phase precipitation in the Fe-Cr-Ni system by a dual-anneal diffusion multiple approach [23]. Nevertheless, there is not yet a method to map the microstructural and mechanical properties for solid-state bulk materials resulting from actual treatment routes or kinetic process.

To face these challenges, we proposed a strategic high throughput methodology, called as kinetic diffusion multiple (KDM), that undergoes interdiffusion annealing to generate continuous composition gradients (particularly suitable at a single-phase region/temperature in order to avoid any extra influence and complexity of possible phase transformation), followed by subsequent realistic thermal treatments like solutioning and/or ageing to trigger favorable phase transformation(s). The resultant blended spectrum of phases and microstructures in the established composition gradients in the KDM will be locally characterized and surveyed by high-spatially resolved electron probe microanalysis (EPMA) and electron back-scattered diffraction (EBSD) while the micromechanical properties can be screened over the established (i.e. indented) composition arrays by advanced micro-nano mechanical testing techniques. Our approach is schematically shown in Fig. 1 together with the conventional diffusion multiple [16].

Section snippets

KDM of quinary Ti alloys

The KDM of quinary titanium alloys, consisting of pure-Ti and the Ti-7.73Al-8.44 V, Ti-7.72Al-8.01Cr and Ti-13.4Al-12.4Mo (wt%) alloy blocks, was designed with its assembled configuration depicted in Fig. 1b. Each composition in the multiple and its position in the assembly were determined to allow a specific diffusion flux between different alloying elements. All four component blocks were machined via electrical discharge machining (EDM) from ingots prepared by arc melting using 99.9% sponge

The composition-microstructure link

Together with the SEM/EBSD observation and EPMA probing of local chemistries, fast quantitative screening of the microstructural characteristics over the well-established composition arrays, i.e. the composition-microstructure link, was sufficed by the KDM. Fig. 2a shows different microstructures in two metallic systems, i.e. Ti on left and Mg on right. The regions with different compositions reveal signature microstructures in the quinary Ti diffusion multiple after solutioning in the β-phase

The composition-microstructure-mechanical properties relationship

Of composition-microstructure and composition-property inter-linked, the KDM technique not only represents a major advance in the measurements/collections of the microstructure and performance information over well-established composition arrays, but also enables a quantitative, rigorous analysis and thorough review of the performance related issues based on the composition-microstructure-mechanical properties relationship collected above. In this work, two specific applications are

Conclusion

In conclusion, we introduced a strategic "kinetic diffusion multiple" (KDM) by applying realistic thermal treatment and then continuous measurement with advanced micro/nano mechanical testing to conventional diffusion multiple. The KDM was demonstrated as a robust methodology and platform that enables rapid screening of the composition-microstructure-micromechanical properties relationships of materials in a high throughput manner. It has also proven successful at elucidating the profound and

Acknowledgements

This work was supported by the Natural Science Funds of China [Grant No. 51571113], International S&T cooperation Program of China (2015DFA51430) and the Joint Project of Industry-University-Research of Jiangsu Province [Grant No: BY2016005]. CW, NL and JW are grateful to the China Scholarship Council (grant number: 201406290011; 201506020081; 201506890002) for financial support. Yi Chen would like to thank the Natural Science Foundation of Jiangsu Province (Grant No. BK20160291) and the

References (44)

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S. Mao and C. Wang contributed equally to this work.

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