The development of NanoSPD as an important area of materials science
The interest in SPD processing was subsequently stimulated by the recognition that it may be used to produce exceptional grain refinement in bulk solids and thus it is a processing tool for achieving unusual and beneficial properties.
Bulk UFG materials:
Additional requirements: fairly homogeneous and reasonably equiaxed microstructures, with a majority of the grain boundaries having high angles of misorientation.
Modern Types of Nanostructured Materials
Two approaches to produce bulk nanostructured materials
1. Bottom-up
由小到大的合成法
Consolidation of nanograins (particles)
一. Introduction
Ultrafine-grained (UFG) materials
Ultrafine-grained (UFG) materials:
polycrystals having very small grains with average grain sizes less than ~1 μm. Thus, the grain sizes of UFG materials lie within the submicrometer (100 –1,000 nm) and nanometer (less than 100 nm) ranges.
Why SPD? To Refine/Homogenize the Microstructure To Strengthen the Material To Enhance the Properties
Examples: Work Hardening Grain Refinement Development of Special Microstructures Development of Special Textures
2. Top-down
Inert gas condensation (惰性气体凝聚原位加压)
– Process • vapour phase of metal • condensed on a cold surface • particles of up to 50 nm in size • consolidation of particles
Segal and coworkers in Minsk, former Soviet Union, 1980s: the technique of equal-channel angular pressing (ECAP) was first introduced in a form that is essentially identical to the procedure now used in many laboratories around the world.
成语：百炼成钢 ancient SPD technique to make good steel. repetitive fold and forgings.
East Han 30 LIAN steel Knife
Thin elongated silicate inclusions in array, indicating the layered microstructure from deformation in the East Han 30 LIAN steel knife.
The development of NanoSPD as an important area of materials science
Severe plastic deformation (SPD) processing has a long history, dating back to the metalworking of ancient China.
As a consequence of this early work, there was a general recognition in the 1990s that SPD processing was becoming an important research area having a significant potential for use in a wide range of industrial applications.
首先制备出纳米颗粒，然后通过原位加压、热等静压、热挤压等 方法制备块体纳米材料。理论上凡是能够获得纳米颗粒的制备方ndensation (Gleiter, 1984) • Electrodeposition (Erb et al, 1989) • Consolidation of nanopowders (Koch,1990) 由大到小的细化法 Decreasing the grain size of already bulk materials • Severe plastic deformation (SPD) (Valiev et al, 1991)
Bulk ultrafine-grained materials processed by severe plastic deformation
郑明毅
哈尔滨工业大学 材料科学与工程学院 2008, 06
Outline
1. Introduction 2. Techniques for SPD Processing 3. Equal channel angular pressing (ECAP) 4. Microstructural features of SPD-processed materials 5. Properties of UFG materials processed by SPD 6. Applications of UFG materials processed by SPD 7. Future prospects for UFG materials by SPD
– Limitations • slow • thin layer (<100 μm)
High energy mechanical milling(高能球磨法)
– Process • metallic particles milled by steel spheres at room or cryogenic T • severe plastic deformation in individual particles • average grain sizes 10-20 nm • consolidation of particles
– Limitations • long time • surface contamination • residual pores in consolidated material • possible coarsening during consolidation
Severe plastic deformaation (SPD)
High Pressure Torsion Equal Channel Angular Pressing (from R.Z. Valiev, Nature Materials 3, 2004)
Why SPD?
Unique feature of SPD processing ：
the high strain is imposed without any significant change in the overall dimensions of the workpiece, the shape is retained by using special tool geometries that prevent free flow of the material and thereby produce a significant hydrostatic pressure. overcoming of a number of difficulties connected with residual porosity in compacted samples, hazardous nano-powders, impurities from ball milling, processing of large scale billets, practical application of the given materials.
Tremendous current interest in SPD processing One of the most active and developing fields in modern materials science: Bulk ultrafine-grained (UFG) materials processed by severe plastic deformation (SPD).
The development of NanoSPD as an important area of materials science