To exanline the deformed microstructures slip lines and twin boundaries in different. Deformation twinning in hexagonal materials xiaozhou liao, jian wang, jianfeng nie, yanyao jiang, and peidong wu due to the scarcity of easy slip systems in hexagonal materials with a hexagonal closepacked structure hcp, deformation twinning plays a crucial role in determining mechanical. The reason for the observed grain size effect on twinning in hcp materials is not clear. Linking energy pathways with deformation behavior of fcc. In the search for new alloys with a great strengthtoweight ratio, magnesium has emerged at the forefront. Alloys are usually stronger than pure metals interstitial or substitutional impurities cause lattice strain. The sfe determines the plastic deformation mechanisms of fcc metals, which switches the deformation mode from dislocation slip to twinning and finally to fcc hcp simt via lowering the sfe. By continuing to use our website, you are agreeing to our use of cookies. It is now well accepted that twin nucleation in fcc materials occurs due to passage of shockley partials over successive 111 planes. In the case of magnesium, the dominant twinning mode 10.
A bifurcated homogeneous nucleation model is presented on the basis of the classical nucleation theory, the shape bifurcation theory and the elastic inclusion model. With a strength rivaling that of steel and aluminum alloys materials which are deployed widely in real world applications today but only a fraction of the density, magnesium holds great promise in a variety of nextgeneration applications. Strength and ductility are correlated with the intrinsic physical and metallurgical variables. To exanline the deformed microstructures slip lines and twin boundaries in different grains of metallic and ceramic specimens. Twin nucleation model based on pn formulation 22 outline. Twinning modes in hcp metals are distinguished by their ability to produce either tensile or compressive strain along the crystallographic caxis, but not both. Twinning plays an important role in accommodating plastic deformation due to the limited number of independent slip systems in hcp metals. Deformation twinning in nanocrystalline materials sciencedirect. The research effort whose results are presented in this paper had as a primary objective the application of a constitutive description for the onset of twinning in conjunction with a constitutive equation for slip to obtain maps for the two regions slip and twinning for a variety of fcc, bcc, and hcp metals. In fact, hcp iron develops a strong crystallographic preferred orientation with the caxis parallel to.
In coarsegrained hcp metals and alloys, twinning is a common deformation mechanism because their small. Significance of mechanical twinning in hexagonal metals at. This is achieved by the passage of dislocations on different glide planes. Deformation twinning is the primary plastic deformation mechanism in several bcc, hcp and low stacking fault energy fcc metals and alloys. Size effect on deformation twinning at the nanoscale in. The deformation twinning from hcp crystals has been heavily researched 1 6 due to the role it plays in the dominant deformation mode and the strengthening mechanism of materials 7 10. The important role of deformation twinning in plastic deformation of h. Deformation twinning mechanisms and modeling in fcc, bcc metals and smas. Grain boundary sliding in higha temperature deformation of. Jan 22, 20 deformation twins deformation or mechanical twins or gliding twins are most prevalent in close packed hexagonal hcp metals e. However, twinning is rarely observed in nc hcp metals and alloys, with the exception of nc zr processed by surface mechanical attrition. The deformation twinning from hcp crystals has been heavily researched due to the role it plays in the dominant deformation mode and the strengthening mechanism of materials. The important role of twinning in plastic deformation is that it causes changes in plane orientation so that further slip can occur.
A higher srs for certain fcc and hcp nanopolycrystals is explained by extrapolation from. Different hexagonal close packed hcp metals are shown to follow either the bcc or fcc case. The case of tita nium and ti alloys, which present basal slip and less twinning activity, is analyzed in a coming paper 51. First principles study of deformation mechanisms in hcp alloys funding source. The deformation twinning from hcp crystals has been heavily.
Various primary and secondary slip and twinning mechanisms can be activated at the same time during the deformation of the hcp materials. Size effect, twinning, hcp metals, lattice strain, molecular dynamics simulations because the number of slip systems in hexagonal closepacked hcp metals is limited, deformation twinning can be favored over dislocation slip. Unfortunately, the twinning mechanisms in hcp metals alloys are still unclear despite extensive studies 20212223, which could be attribute to the changes of the energy pathway for. Novel corich high entropy alloys with superior tensile. Basics of deformation twinning in fcc metals deformation twinning as a common deformation mechanism has been described in textbooks53 as well as specialized books dealing with dislocations and deformation of metals54. In magnesium and its alloys, two types of caxis twins are.
In cubic metals arbitrary changes in shape can be completely accommodated by easy slip, and twins form as a result of glide processes. The surface along which the lattice points are shared in twinned crystals is called a composition surface or twin plane. However, the twining behavior in nc bcc and hcp metals have not been well studied, although it is generally observed that nc hcp metals are more dif. Deformation twinning mechanisms and modeling in fcc. In magnesium and its alloys, two types of caxis twins are frequently reported, 1012 1011 tension.
Download pdf 8236k download meta ris compatible with endnote, reference. Twinning is the result of identical motions of atoms of a plurality of rows parallel to a twinning plane in the original lattice. Deformation twinning mechanism in hexagonalclosepacked crystals. Here we will only brie y describe some selected aspect of it to help with the discussions in the following sections of. The result is an intergrowth of two separate crystals in a variety of specific configurations. Chapter outline dislocations and strengthening mechanisms. Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. Walley2 the high strain rate dependence of the flow stress of metals and alloys is described from a dislocation mechanics viewpoint over a range beginning from conventional tensioncompression. This is a pdf file of an unedited manuscript that has been accepted for publication. Application to magnesium alloys abstract biography friday, january 27, 2017 3. On the mechanistic basis of deformation at the microscale. It would be scientifically and technically important to activate deformation twinning in nc hcp metals. Jun 18, 2018 twinning has been experimentally seen in highentropy alloys, but understanding how it operates remains a challenge.
Easy slip along does not provide for deformation along 0001. Deformation twinning in a nanocrystalline hcp mg alloy. A variational constitutive model for sliptwinning interactions in hcp metals. Deformation twins deformation or mechanical twins or gliding twins are most prevalent in close packed hexagonal hcp metals e. Thus, hcp metals possess much lesser ductility than fcc metals. Twinning has been experimentally seen in highentropy alloys, but understanding how it operates remains a challenge.
Slip, twinning, and fracture in hexagonal closepacked metals. Acoustic emission ae, the phenomenon whereby transient elastic waves are generated by the. A clustertype grain interaction deformation texture model accounting for twinninginduced texture and strainhardening evolution. Sep, 2006 the important role of deformation twinning in plastic deformation of h. Twinning in bcc metals part 2 twinning stress in smastwin nucleation model. Modeling of deformation behaviour of hcp metals using. Pdf due to the scarcity of easy slip systems in hexagonal materials with a hexagonal. Internal strain and texture evolution during deformation. Sep 04, 2018 the important role of twinning in plastic deformation is that it causes changes in plane orientation so that further slip can occur.
Twinning can cause compression, or extension along the caxis depending on the ca ratio of the metal. Hexagonal closepacked hcp metals 1 are used in a wide variety of engineering sectors, including aerospace, nuclear, automotive, scientific instrumentation, chemical engineering and bioengineering. Plastic deformation of metallic alloys usually takes place through slip, but occasionally involves twinning. In coarsegrained fcc and bcc materials, stacking faults and deformation twins usually occur in metals and alloys with low stacking fault energy, although high strain rate and low deformation temperature can significantly promote twinning. Dislocations and plastic deformation 9motion of dislocations in response to stress 9slip systems 9plastic deformation in single crystals polycrystalline materials strengthening mechanisms 9grain size reduction 9solid solution strengthening 9strain hardening recovery, recrystallization, and grain growth not tested. Much research has been devoted to model deformation of hexagonal metals using polycrystal plasticity theory. Contribution to the study of deformation twinning in titanium. Doitpoms tlp library superelasticity and shape memory. Please redirect your searches to the new ads modern form or the classic form. Twinning plays role in the critical deformation of hexagonal closepacked hcp metals. Developing hcp alloys with improved properties requires a fundamental knowledge on the twinning mechanisms which, however, remain largely theoretical contentions. Size effect on deformation twinning at the nanoscale in hcp metals.
Alloy deformation ghazisaeidi studies hcp alloys for theoretical, industrial applications project lead. Ratedependent hardening model for hcp metals with effect. High strain rate properties of metals and alloys r. While deformation by slip mechanisms is reasonably well understood, less remains known about deformation by twinning. Roles of slip and twinning on indentation formations in. Developing hcp with improved alloys properties requires a fundamental knowledge on the twinning mechanisms which, however,remain largely theoretical contentions.
The potentially active deformation modes to be considered here are those reported by tenckhoff. Intrinsic rotationangle fluctuations of twinning in hcp. The metals and alloys are used owing to the combination of excellent mechanical properties, corrosion resistance and the ability to engineer new. While deformation by slip mechanisms is reasonably well understood, less remains known about deformation by. This results in an optimum grain size that is easiest to deform by twinning for fcc metals 40, 42. Dependingupontheca axialratio,hcptwinningmodes may be either tensile or compressive 14. The details of a number of phenomena relevant to twinning, including the microstructure of tbs, the tb migration characteristics, and the twin nucleation remain obscure due. Abstract the important role of deformation twinning in plastic deformation of h. Twinning is the result of identical motions of atoms of a plurality of rows parallel to a twinning plane in the.
Atomicscale in situ tem investigation of deformation. Intrinsic rotationangle fluctuations of twinning in hcp mg. Twinning plays critical role in the deformation of hexagonal closepacked hcp metals. On the other hand, twinning in tial becomes active at temperatures around 750800 c where slip by ordinary and superlattice dislocations takes place, but not at lower temperatures where glide by superlattice dislocations dominate. Here, the authors show that twinning can be a primary deformation mechanism in.
Size effect on deformation twinning at the nanoscale in hcp. Grain size effect on deformation twinning and detwinning. Mechanical twinning occurs in metals that have bodycentered cubic bcc and hexagonal close packed hcp crystal structures, at low temperatures, and at high rates of loading shock loading, conditions under. Deformation twinning mechanism in hexagonalclosepacked. Hanyang university, south korea korea atomic energy research institute. Progress in materials science deformation twinning in. Here, by using stateoftheart in situ transmission electron microscopy, the atomic mechanisms of twinning. Law of atomic motion during 1011 twinning in magnesium alloys. Deformation twinning mechanisms and modeling in fcc, bcc. Slip occurs when crystal planes glide past each other. Twinning plays an important role in the plastic deformation of hexagonal closepacked hcp metals such as mg alloys, because of their limited number of slip sy we use cookies to enhance your experience on our website. The objective of this research is to study the deformation mechanisms associated with twinning in. Deformation twins are the result of stress on the crystal after the crystal has formed.
The twin plane is a boundary which separates two orierltations that are mirror images of one another. Deformation twinning in hexagonal materials mrs bulletin. In this work we have focussed on twinning in fcc alloys. In particular, twinning is important in hexagonal close packed materials where the easy slip systems are insufficient to accommodate arbitrary deformations. While deformation by slip mechanisms is reasonably well. Slip and twinning are the two fundamental modes by which metals and alloys can deform plastical1y. Most of the tests were conducted in compression and at temperatures between 77 and k. There has been little previous work on the hightemperature deformation of directionally solidi. Basics of deformation twinning in fcc metals deformation twinning as a common deformation mechanism has been described in textbooks53 as well as specialized books dealing with dislocations and deformation of metals 54. In particular, twinning is important in hexagonal close packed.
Zr alloys, the main domains of crsss which lead to qualitatively different textures. The predominant deformation twinning mechanism in all hcp metals is the 10. Mechanisms of plastic deformation and acoustic emission in. To demonstrate the mechanisms of deformation in bcc, fcc, and hcp structure metals and alloys and in some ceramics as well. Plastic deformation of metallic alloys usually takes place through slip, but. Due to the scarcity of easy slip systems in hexagonal materials with a hexagonal closepacked structure hcp, deformation twinning plays a crucial role in determining mechanical properties and texture evolution. Deformation twinning in hexagonal materials mrs bulletin volume 41 april 2016 w w w.
Texture development in polycrystals depends on the active deformation mechanisms. Twinning induced nanostructure formation during cryo. As only a small fraction of the volume gets twinned, the amount of total deformation is less. Metals with hcp structures have reduced number of available slip systems compared to cubic structures, making plastic deformation more difficult. On the other hand, f1012 g twins occur in caxis compression in zinc, whose ca 1. Deformation behavior of hcp tial alloy single crystals. Pdf deformation twinning in hexagonal materials researchgate. Ratedependent hardening model for hcp metals with effect of deformation twinning and dynamic recrystallization 6 th international conference and exhibition on materials science and engineering september 1214, 2016 atlanta, usa. The objective of this research is to study the deformation mechanisms associated with twinning in hcp metals magnesium and zirconium alloys. Trace analysis of prepolished surfaces enabled identification of the twin or slip. Size effect, twinning, hcp metals, lattice strain, molecular dynamics simulations. Since in twinning only a small movement of atoms occurs and it is a cooperative process it can occur much more quickly than slip, making it much more common in high stress rate situations. The details of a number of phenomena relevant to twinning, including the microstructure of tbs, the tb migration characteristics, and the twin nucleation.
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