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