scholarly journals Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility

2015 ◽  
Vol 112 (47) ◽  
pp. 14501-14505 ◽  
Author(s):  
Xiaolei Wu ◽  
Muxin Yang ◽  
Fuping Yuan ◽  
Guilin Wu ◽  
Yujie Wei ◽  
...  
Keyword(s):  
Large Scale ◽  
Low Cost ◽  
High Strength ◽  
Back Stress ◽  
Coarse Grained ◽  
Ultrafine Grain ◽  
Asymmetric Rolling ◽  
Dislocation Hardening ◽  
Ultrafine Grained ◽  
Lamella Structure

Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.

Grain Refinement and Deformation Behavior of Ultrafine Grained Pd and Pd-Ag Alloys Produced by HPT

2008 ◽  
Vol 584-586 ◽  
pp. 182-187
Author(s):  
Lilia Kurmanaeva ◽  
Yulia Ivanisenko ◽  
J. Markmann ◽  
Ruslan Valiev ◽  
Hans Jorg Fecht
Keyword(s):  
Mechanical Properties ◽  
Deformation Behavior ◽  
Materials Science ◽  
High Pressure Torsion ◽  
Uniform Elongation ◽  
Grain Structure ◽  
Coarse Grained ◽  
Ultrafine Grain ◽  
Ultrafine Grained ◽  
Ultrafine Grain Structure

Investigations of mechanical properties of nanocrystalline (nc) materials are still in interest of materials science, because they offer wide application as structural materials thanks to their outstanding mechanical properties. NC materials demonstrate superior hardness and strength as compared with their coarse grained counterparts, but very often they possess a limited ductility or show low uniform elongation due to poor strain hardening ability. Here, we present the results of investigation of the microstructure and mechanical properties of nc Pd and Pd-x%Ag (x=20, 60) alloys. The initially coarse grained Pd-x% Ag samples were processed by high pressure torsion, which resulted in formation of homogenous ultrafine grain structure. The increase of Ag contents led to the decrease of the resulted grain size and change in deformation behavior, because of decreasing of stacking fault energy (SFE). The samples with larger Ag contents demonstrated the higher values of hardness, yield stress and ultimate stress. Remarkably the uniform elongation had also increased with increase of strength.

scholarly journals Aging Behaviour of Al-Mg-Si Alloys Subjected to Severe Plastic Deformation by ECAP and Cold Asymmetric Rolling

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
S. Farè ◽  
N. Lecis ◽  
M. Vedani
Keyword(s):  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Isothermal Aging ◽  
Room Temperature ◽  
Coarse Grained ◽  
Peak Shape ◽  
Asymmetric Rolling ◽  
Ultrafine Grained ◽  
Aging Kinetics ◽  
Reduced Intensity

A study was carried out on aging behaviour of a 6082 alloy processed by two different severe plastic deformation techniques: ECAP and asymmetric rolling. Both techniques were able to generate an ultrafine-grained structure in samples processed at room temperature. It was stated that severe straining promotes marked changes in the postdeformation aging kinetics. The peaks of β′′/β′ transition phases were anticipated and of progressively reduced intensity over the coarse grained alloy. A further peak accounting for onset of recrystallization also appeared in the most severely deformed samples. Full consistency in peak shape and position was found when comparing materials processed by ECAP and asymmetric rolling. Isothermal aging treatments performed at 180°C revealed that in the severely deformed samples, aging became so fast that the hardness curves continuously decreased due to overwhelming effects of structure restoration. On the contrary, aging at 130°C offers good opportunities for fully exploiting the precipitate hardening effects in the ultrafine-grained alloy.

Synthesis of high-strength W–Ta ultrafine-grain composites

2008 ◽  
Vol 23 (1) ◽  
pp. 133-139 ◽  
Author(s):  
R.T. Ott ◽  
X.Y. Yang ◽  
D.E. Guyer ◽  
S. Chauhan ◽  
D.J. Sordelet
Keyword(s):  
High Strength ◽  
High Energy ◽  
High Temperature Phase ◽  
High Yield ◽  
Ultrafine Grain ◽  
Temperature Phase ◽  
Composite Powders ◽  
Ultrafine Grained ◽  
Submicron Scale ◽  
The Individual

Bulk samples of an ultrafine-grained tungsten–tantalum composite alloy have been synthesized by consolidating mechanically milled composite powders. The grain growth during densification is limited due to the submicron-scale layering of the individual metals in the composite particles and the relatively low sintering temperature (1300 °C). The ultrafine microstructure of the high-density (∼99% theoretical density) samples leads to a high yield stress of ∼3 GPa under quasi-static uniaxial compression. A tendency for Ta-rich solid-solution formation during densification was observed, and the high-temperature phase equilibria in the composite powders were examined further using high-energy x-ray diffraction at temperatures up to 1300 °C.

Influence of Severe Plastic Deformation on Mechanical Properties of an AA5024 Alloy

2016 ◽  
Vol 879 ◽  
pp. 1317-1322 ◽  
Author(s):  
Anna Mogucheva ◽  
Diana Yuzbekova ◽  
Tatiana Lebedkina ◽  
Mikhail Lebyodkin ◽  
Rustam Kaibyshev
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
High Strength ◽  
Coarse Grained ◽  
Type B ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Elongation To Failure ◽  
Dislocation Strengthening

The paper reports on the effect of severe plastic deformation on mechanical properties of an Al-4.57Mg-0.35Mn-0.2Sc-0.09Zr (in wt. pct.) alloy processed by equal channel angular pressing followed by cold rolling (CR). The sheets of the 5024 alloy with coarse grained (CG) structure exhibited a yield stress (YS) near 410 MPa and an ultimate tensile strength (UTS) of 480 MPa, while the YS and UTS of this material with ultrafine-grained (UFG) structure increased to 530 and 560 MPa, respectively. On the other hand, the elongation to failure decreased by a factor of 2 and 4 after CR and CR following ECAP, respectively. It was shown that dislocation strengthening attributed to extensive CR plays a major role in achieving high strength of this alloy. Besides these macroscopic characteristics, jerky flow caused by the Portevin-Le Chatelier (PLC) instability of plastic deformation was examined. The formation of UFG structure results in a transition from mixed type A+B to pure type B PLC serrations. No such effect on the serrations type was observed after CR.

scholarly journals Особенности упрочнения структурированного интенсивной пластической деформацией сплава Al-Cu-Zr

2021 ◽  
Vol 63 (10) ◽  
pp. 1572
Author(s):  
Т.С. Орлова ◽  
Д.И. Садыков ◽  
М.Ю. Мурашкин ◽  
В.У. Казыханов ◽  
Н.А. Еникеев
Keyword(s):  
High Pressure Torsion ◽  
High Strength ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
Microstructural Parameters ◽  
Transmission Electron ◽  
Ultrafine Grained ◽  
Preliminary Annealing ◽  
Coarse Grained State ◽  
Additional Hardening

The effect of small additions of copper on the microstructure and physic-mechanical properties of an ultrafine-grained Al-1.47Cu-0.34Zr (wt%) alloy structured by high pressure torsion after preliminary annealing at 375 °C for 140 h has been studied. As a result of processing, high values of strength characteristics (conditional yield strength 430 MPa, ultimate tensile strength 574 MPa) with an acceptable level of electrical conductivity (46.1% IACS) and ductility (elongation to fracture ~ 5%) have been achieved. On the basis of the microstructural parameters determined by X-ray diffraction analysis and transmission electron microscopy, hardening mechanisms responsible for such high strength have been analyzed. It was shown that Cu plays the key role in strengthening. The addition of copper significantly contributes to grain refinement and, consequently, to grain-boundary hardening. Alloying with copper leads to significant additional hardening (~ 130 MPa) in the ultrafine-grained alloy, which is not typical for coarse-grained state. Segregation of Cu at grain boundaries and the formation of Cu nanoclusters are the most probable reasons for this hardening.

Investigation of Possible Mechanisms for Developing Long Steel Products with Ultrafine Grained Microstructure

2014 ◽  
Vol 783-786 ◽  
pp. 744-749
Author(s):  
Claudio Guarnaschelli ◽  
Ilaria Salvatori ◽  
Tommaso Coppola
Keyword(s):  
Process Parameters ◽  
Hot Rolling ◽  
High Strength ◽  
Ultrafine Grain ◽  
Rolling Mills ◽  
Size Refinement ◽  
Ultrafine Grained ◽  
Austenite Recrystallization ◽  
Environmentally Friendly Process ◽  
New Generation

The obtainment of ultrafine grain microstructures, by the application of process parameters which are potentially feasible under industrial conditions, is attractive to develop a new generation of low alloy steel (Ultrafine Grain Steel, UFG) characterized by high strength and toughness, good cold/warm formability, environmentally-friendly process. The ferrite grain size refinement beyond existing levels by means of hot rolling mills, without requiring drastic plant changes, can be achieved by lowering the rolling temperature down to the range Ae3 - Ar3 in the finishing stands. In this temperature range different metallurgical mechanisms may take place. Austenite recrystallization is slower and there is a greater chance of obtaining non-recrystallized deformed austenite (pancake), which after phase transformation will give finer ferrite (Heavy Gamma Deformation). Or, in alternative, Deformation Induced Ferrite Transformation can occur especially in C-Mn steels, promoting the formation of ultrafine ferrite grains (DIFT). Most of the existing studies on UFG steel focus on flat products. In this paper the mechanisms to be exploited for producing UFG long products are identified and examined on different low and medium carbon non-alloyed steels, as the common grades used for fastener applications. In particular, Heavy Gamma Deformation and DIFT are investigated through laboratory tests aimed at determining the process parameters affecting the two mechanisms in different ranges of chemical composition. On the basis of the results found, some basic concepts for industrialization on modern hot rolling mills will be given.

scholarly journals A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 598 ◽  
Author(s):  
Yan Ma ◽  
Muxin Yang ◽  
Fuping Yuan ◽  
Xiaolei Wu
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Back Stress ◽  
Coarse Grained ◽  
Strain Partitioning ◽  
Challenges And Opportunities ◽  
New Strategy ◽  
Future Challenges ◽  
Superior Mechanical Properties ◽  
Strength And Ductility

Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures in metals have been proven to be a new strategy to achieve unprecedented mechanical properties that are not accessible to their homogeneous counterparts. Here, we review recent advances in overcoming this strength–ductility trade-off by the designs of several heterogeneous nanostructures in metals: heterogeneous grain/lamellar/phase structures, gradient structure, nanotwinned structure and structure with nanoprecipitates. These structural heterogeneities can induce stress/strain partitioning between domains with dramatically different strengths, strain gradients and geometrically necessary dislocations near domain interfaces, and back-stress strengthening/hardening for high strength and large ductility. This review also provides the guideline for optimizing the mechanical properties in heterogeneous nanostructures by highlighting future challenges and opportunities.

Description of the Superplastic Flow Process by Deformation Mechanism Maps in Ultrafine-Grained Materials

2016 ◽  
Vol 838-839 ◽  
pp. 51-58 ◽  
Author(s):  
Megumi Kawasaki ◽  
Terence G. Langdon
Keyword(s):  
Deformation Mechanism ◽  
Elevated Temperatures ◽  
High Pressure Torsion ◽  
Processing Technique ◽  
Superplastic Flow ◽  
Coarse Grained ◽  
Ultrafine Grain ◽  
Flow Process ◽  
Ultrafine Grained ◽  
Wide Range

The synthesis of ultrafine-grained (UFG) materials is very attractive because small grains lead to excellent creep properties including superplastic ductility at elevated temperatures. Severe plastic deformation (SPD) is an attractive processing technique for refining microstructures of metallic materials to have ultrafine grain sizes within the submicrometer to even the nanometer level. Among the SPD techniques, most effective processing is conducted through equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) and there are numerous reports demonstrating the improved tensile properties at elevated temperature. This report demonstrates recent results on superplasticity in metals after ECAP and HPT. Moreover, superplastic flow of the UFG materials is evaluated by using flow mechanisms developed earlier for coarse-grained materials and depicted by plotting deformation mechanism maps which provide excellent visual representations of flow properties over a wide range of testing conditions.

scholarly journals Introduction to Heterostructured Materials: A Fast Emerging Field

2021 ◽  
Author(s):  
Yuntian Zhu
Keyword(s):  
Large Scale ◽  
Materials Science ◽  
Low Cost ◽  
Back Stress ◽  
Industrial Facilities ◽  
Electric Cars ◽  
Aerospace Applications ◽  
Fast Development ◽  
Superior Mechanical Properties ◽  
Collaborative Efforts

AbstractStrong and tough materials are desired for lightweight, energy efficient applications such as electric cars and aerospace applications. Recently, heterostructures are found to produce unprecedented strength and ductility that are considered impossible based on the materials science in our textbooks. Such superior mechanical properties are enabled by a new scientific principle: hetero-deformation-induced (HDI) strengthening and work hardening. Heterostructured (HS) materials consist of heterogeneous zones with dramatic difference (> 100 pct) in flow stresses. The inter-zone interaction produces back stress in the soft zones and forward stress in the hard zones, which collectively produces the HDI stress. HS materials possess a significant synergistic effect where the integrated property exceeds the prediction by the rule of mixtures. Importantly, HS materials can be produced by current industrial facilities at large scale and low cost. The new materials sciences and promising applications are driving the fast development of the HS materials as an emerging field. There are many fundamental issues that need to be probed so as to effectively design HS materials for superior properties. To solve these issues, it requires collaborative efforts by the communities of experimental materials science and computational material science and mechanics.

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