Microstructure and texture of high manganese steel subjected to dynamic impact loading

ABSTRACT

Dynamic impact response of high Mn-steel at a strain rate of 3000?s^?1 was investigated using the Split Hopkinson Pressure bar. The investigated steel depicted continuous yielding at high strain rates. Additionally, the yield stress displayed a positive strain-rate sensitivity with an increasing strain rate. Microstructural evaluations displayed that strain-induced martensitic transformation and dislocation multiplication during slip were dominant plastic deformation mechanisms in the absence of deformation twinning which contributes to the strain hardening. Adiabatic shear band and martensite to austenite reversion or dynamic recrystallisation were also attributed to strain softening during impact deformation. The {001}<110> R-cube, {011}<110> R-Goss, and ({111}<110>) E texture components were strengthened after impact loading compared with as-received condition, while the intensities of Cube, Cupper, Brass, and S texture components were decreased.     

Influences of Thermal Martensites and Grain Orientations on Strain-induced Martensites in High Manganese TRIP/TWIP Steels

Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction(XRD),scanning electron microscopy(SEM) and electron backscattered diffraction(EBSD).Before deformation,the morphology of α’-M depended mainly on the number of variants and growing period.Regardless of martensite morphologies and deformation,the Kurdjumov-Sachs(K-S) orientation relationships always maintained.The 6 α-M variants formed from a plate of ε-M were of 3 pairs of twins with a common axis <110> α’ parallel to the normal of {111} γ habit plane to minimize transformation strain.When α’-M could be formed only by deformation,it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates.Thick ε plates promoted significantly the α’-M and weakened the influence of grain orientations.During tension,the transformation in <100>-oriented grains was observed to be slower than that in <111>-oriented grains.Deformation twins promoted ε-M formation slightly and had no apparent effect on α’-M.Deformation increased the number of ε-M variants,but reduced that of α’-M variants.     

Thermodynamic modeling of the initial microstructural evolution of oxide films grown on bare copper

A thermodynamic model is presented that predicts the initial growth of either a (semi-) coherent crystalline oxide phase or an amorphous oxide phase (with a subsequent amorphous-to-crystalline transition) on a bare metal as function of the substrate orientation, growth temperature and film thickness. The model accounts for possible relaxation of growth stresses by plastic deformation. The direct formation and growth of semi-coherent, crystalline Cu₂O is predicted by application of the model to oxide overgrowth on bare Cu{111}, Cu{100} and Cu{110}. For oxide overgrowths on Cu{111} and Cu{110}, a square grid of misfit dislocations with a dislocation distance of about six Cu₂O unit cells would occur on the basis of the model calculations, which agrees with experimental observations reported for Cu{111} in the literature. On Cu{100} an array of misfit dislocations is formed along the single direction of high lattice mismatch.     

High strain rate behavior, transformation-induced plasticity and fracture toughness characterization of cast and additionally tempered Fe85Cr4Mo8V2C1 alloy manufactured using a rapid solidification technique

This study focuses on the characterization of the microstructures of an FeCrMoVC alloy in two states (an as-cast and a heat-treated state) as well as the compressive strain rate-dependent material and fracture toughness behavior. Both microstructures consist of martensite, retained austenite and complex carbides. Tempering results in a transformation of retained austenite into martensite, the precipitation of fine alloy carbides, and diffusion processes. High yield stresses, flow and ultimate compressive strength values at a relatively good deformability were measured. The yield and flow stresses at the onset of deformation are higher for the heat-treated state due to higher martensitic phase fractions and fine precipitations of alloy carbides respectively. Compressive deformation causes a strain-induced transformation of retained austenite to α′-martensite. Hence, both high-strength alloys are TRIP-assisted steels (TRansformation-Induced Plasticity). However, the martensitic transformation is more pronounced in the as-cast state due to higher phase fractions of retained austenite already in the initial state. Examinations of strained microstructures showed decreased crystallite sizes with increasing deformation. It is assumed that, during plastic deformation, the amount of low angle grain boundaries increases while the incremental formation of α′-martensite leads to decreased crystallite size. In general, lower microstrains were determined in the heat-treated state as a consequence of stress relaxation during tempering. In comparison to commercially available tool steels, the determined fracture toughness K _Ic of both variants revealed relatively high fracture toughness values. It was found that the lower shelf of K _Ic is already reached at room temperature. Higher loading rates $ \dot{K} $ resulted in lower dynamic fracture toughness K _Id values. Notch fracture toughness K _A measurements indicate that the critical notch tip radii of the examined materials are slightly smaller than 0.09?mm.     

Deformation and fracture of Al-8Fe rapidly solidified alloys

The effects of the rapid solidification on the deformation and fracture of Al-8Fe alloys, from TEM fracture specimens, have been studied. The most general conclusion which can be drawn in this study is clearly in agreement with a plastic deformation mechanism. Crack propagation occurs by localized plastic rupture mechanisms which result from enhanced slip along {111} planes. Crack propagation occurs within the deformed zone either by the nucleation, growth and coalescence of holes ahead of the crack-tip, or through the emission of dislocation from the crack-tip. The resulting fracture is along the active {111} slip planes. The principal effect of secondary phases (Al₁₃Fe₄) on the fracture propagation in Al-8Fe alloys was that the secondary phases increased the stress level at which plastic deformation occurs at the crack-tip and increased the stress level at which the crack propagates. This work clearly shows that in order to obtain coarse intermetallic precipitates in the specimens after ageing heat treatments the crack propagation and deformation processes occur at lower stresses compared to as-received rapidly solidified samples.     

The Ideal Strengths of Superconducting MgCNi<Subscript>3</Subscript> and CdCNi<Subscript>3</Subscript>

The stress-strain curves under tensile deformation in the 〈100〉, 〈110〉, and 〈111〉 directions and under shear deformation in the (001)〈110〉, \((110)\langle \overline {1}10\rangle \), \((111)\langle 1\overline {1}0\rangle \), and \((111)\langle 11\overline {2}\rangle \) slip systems have been systematically calculated by first-principles method to study the ideal strengths of superconducting MgCNi₃ and CdCNi₃. The ideal strengths in the three tensile directions are found to be reduced in the order of 〈100〉 → 〈110〉 → 〈111〉 and those for the four shear slip systems in the order of \((110)\langle \overline {1}10\rangle \rightarrow (111)\langle 11\overline {2}\rangle \rightarrow (111)\langle 1\overline {1}0\rangle \rightarrow (001)\langle 110\rangle \) for both superconductors. Their lowest ideal tensile strengths are found to be larger than the corresponding highest ideal shear strengths, which could explain why both superconductors have the ductility. The obtained lattice constants and elastic properties coincide well with the the available experimental and theoretical values.     

Twinning in TiAl

The results of this investigation are in agreement with the findings of Richards and Cahn which show that the formation of twin-related TiAl regions, TiAl_T, and the Ti₃Al phase, rather than TiAl deformation twins, will be favored energetically in a two-phase titanium aluminide alloy. Due to the formation of Ti₃Al at the TiAl_T interface, all possible {111}<112> TiAl_T, as opposed to only {111}[112] deformation twins, can be formed within TiAl lamellae without the destruction of the symmetry of L1₀ structure.     

Heterogeneous nucleation of solidification of cadmium particles embedded in an aluminium matrix

A hypomonotectic alloy of Al-4.5wt%Cd has been manufactured by melt spinning and the resulting microstructure examined by transmission electron microscopy. As-melt spun hypomonotectic Al-4.5wt%Cd consists of a homogeneous distribution of faceted 5 to 120 nm diameter cadmium particles embedded in a matrix of aluminium, formed during the monotectic solidification reaction. The cadmium particles exhibit an orientation relationship with the aluminium matrix of {111}_Al//{0001}_Cd and 110_AlAl//11¯20> _Cd, with four cadmium particle variants depending upon which of the four {111}_Al planes is parallel to {0001}_Cd. The cadmium particles exibit a distorted cuboctahedral shape, bounded by six curved {100}_Al//{20¯23}_Cd facets, six curved {111}_Al/{40¯43}_Cd facets and two flat {111}_Al//{0001}_Cd facets. The as-melt spun cadmium particle shape is metastable and the cadmium particles equilibrate during heat treatment below the cadmium melting point, becoming elongated to increase the surface area and decrease the separation of the {111}_Al//{0001}_Cd facets.The equilibrium cadmium particle shape and, therefore, the anisotropy of solid aluminium-solid cadmium and solid aluminium -liquid cadmium surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 420 °C. The anisotropy of solid aluminium-solid cadmium surface energy is constant between room temperature and the cadmium melting point, with the {100}_Al//{20¯23}_Cd surface energy on average 40% greater than the {111}_Al//{0001}_Cd surface energy, and 10% greater than the {111}_Al//{40¯43_Cd surface energy. When the cadmium particles melt at temperatures above 321 °C, the {100}_Al//{20¯23}_Cd facets disappear and the {111}_Al//{40¯43}_Cd and {111}_A1//{0001}_Cd surface energies become equal. The {111}_Al facets do not disappear when the cadmium particles melt, and the anisotropy of solid aluminium-liquid cadmium surface energy decreases gradually with increasing temperature above the cadmium melting point.The kinetics of cadmium solidification have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Cadmium particle solidification is nucleated catalytically by the surrounding aluminium matrix on the {111}_Al faceted surfaces, with an undercooling of 56 K and a contact angle of 42 °. The nucleation kinetics of cadmium particle solidification are in good agreement with the hemispherical cap model of heterogeneous nucleation.     

Formation of {111} fibre texture in recrystallised aluminium sheet

Abstract

The deep drawability of commercial purity aluminium sheets is improved by introducing a (in fcc materials rather unusual) {111} fibre texture in the sheet surface layers. An additional step of warm rolling after the conventional hot and cold rolling leads to the formation of a pronounced shear texture in the sheet surface layers. During the final recrystallisation annealing, the desired {111} texture prevails at the expense of the other shear texture components. The present paper aims to clarify the mechanisms of the formation of {111}∥ND orientations during both warm rolling and recrystallisation. The effect of the {111} surface texture on the plastic anisotropy of the resulting sheets is discussed.     

Isothermal transformation and decomposition ofβ 1 phase in a CuZnAl alloy

In the present paper, the crystallography of isothermal transformation and decomposition ofβ, phase have been studied by means of transmission electron microscopy and diffraction in the CuZnAl shape memory alloy. It has been proved that the bainite formed inβ ₁, matrix when the samples were transformed isothermally at moderate temperature. The crystallography of the isothermal bainitic transformation is identical to that of martensite in the same system. When the specimens were aged at moderate temperatures for longer time, the bainite and matrix decomposed to equilibrium phases. The decomposition process can be summarized as follows: $$\begin{gathered} bainite (9R) \to 9R + \alpha \left( {fcc} \right) \to \alpha + \beta \left( {bcc} \right) \hfill \\ matrix (B2) \to 2H + B2 \to \beta \left( {bcc} \right) \hfill \\ \end{gathered} $$ There are definite orientation relationships among these phases during the decomposition process and they are shown below: $$\begin{gathered} \left( {111} \right)_\alpha \parallel \left( {001} \right)_B ,\left[ {0\bar 11} \right]_\alpha \parallel \left[ {\bar 110} \right]_B \hfill \\ \left( {111} \right)_\alpha 5^ \circ away from \left( {110} \right)_\beta ,\left[ {0\bar 11} \right]_\alpha \parallel \left[ {1\bar 1\bar 1} \right]_\beta \hfill \\ \left( {110} \right)_M \parallel \left( {001} \right)_{2H} ,\left[ {001} \right]_M \parallel \left[ {010} \right]_{2H} \hfill \\ \end{gathered} $$ Thus, the crystallography of isothermal transformation and decomposition ofβ ₁ phase and the sequence of transitions have been revealed.     

Deformation and fracture of germanium single crystals

Diamond-pyramid indentations, made with loads of 1 to 100 g at room temperature on {111}, {110} and {112} faces of germanium crystals, were studied by scanning electron microscopy. The Vickers-hardness number, which was highest for {111} faces, increased with the square root of the load by a factor of about 10 on any given surface, ranging from values as low as 60 to about 850, the latter corresponding to the VHN reported in the literature. The lengths of major cracks, generally seen on the surface of the crystal as an extension of the indentation diagonals, were found to be proportional tod-d ₀, whered ₀, equal to about 3 μm, represents a lower limiting value of the indentation diagonald, below which cracks do not seem to form. The increase of the VHN and of the crack-lengths with load is explained in terms of a tentative model involving the formation and the stress-induced growth of laminar “plastic” patches in a volume surrounding the indentation.     

Understanding the yield behaviour of L12-ordered alloys

Nickel superalloys exhibit a remarkable characteristic. Their yield stress that required to cause the onset of plastic deformation increases with temperature. This typically occurs up to a temperature of around 800°C. This effect is thought to originate from the precipitates of the microstructure, which have an L1₂-ordered crystal structure. A number of other L1₂-based alloys exhibit similar yield properties. It is generally accepted that this is caused by the exhaustion of dislocations by cross-slip from {111} glide planes to {010} planes on which they are sessile. However, the underlying mechanisms that control this cross-slipping process are yet to be fully understood, with little consistency between empirical results and theory. A critical review of the various theories surrounding nickel superalloys is offered.     

Microstructure and texture of Al coating during kinetic spraying and heat treatment

Microstructure and texture formation of an Al coating during kinetic spraying (or cold gas dynamic spraying) and heat treatment were investigated. Coating formation by kinetic spraying is based on super-sonic collision of in-flight micron-sized particles and their severe interfacial plastic deformation under ultra-high strain rates (1.0 × 10⁶–0.5 × 10⁹ s⁻¹), which induces adiabatic shear instability. Shear texture, 45°-rotated Cube {001} <110>, and static recovered microstructure were formed at the interface of Al during kinetic spraying because Al has the equivalent slip system {111} <110> of a face-centered cubic having high stacking fault energy (SFE). During heat treatment, discontinuous recrystallization and grain growth led to transformation of the shear texture into a strong Cube texture, {001} <100>, and misorientation angle transition. Given the mechanical and physical properties of the Al, metallurgical mechanisms of microstructure and texture formation of kinetic-sprayed and heat-treated Al coatings were suggested based on transmission electron microscopy and electron backscatter diffraction analysis.     

Unraveling the origin of strain-induced precipitation of M23C6 in the plastically deformed 347 Austenite stainless steel

In this research, the phenomenon of strain-induced precipitation of M₂₃ (M = Cr, Fe, Mo) C₆ precipitates in 347 austenite stainless steel was systematically studied. During annealing at 650 °C, the experimental results exhibited significantly earlier formation of M₂₃C₆ precipitates in the plastically strained specimen, than in the no-strain specimen. The various microstructural characterizations showed that the accelerated formation of M₂₃C₆ precipitates occurred around deformation bands that were generated by deformation twinning. Extensive investigation suggested that the strain-induced precipitation of M₂₃C₆ is attributed to the formation of strain-induced α′ martensite during plastic deformation near deformation bands.     

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

Plastic deformation and “work-hardening” of diamond

Extensive plastic deformation of diamond crystals can be accomplished by squeezing diamond embedded in diamond powder at high pressures and temperatures. By inhibiting brittle fracture, deformation takes place at temperatures as low as 900°C at 60kb. The {111} deformation lamellae have a higher abrasion resistance than even the {111} plane of diamond.     

Stabilization of the NiF2 orthorhombic phase in epitaxial heterostructures on CaF2/Si(111) substrates

Epitaxial NiF2 layers have been grown for the first time on CaF₂(111)/Si(111) substrates by molecular beam epitaxy. By high-energy electron diffraction and X-ray diffractometry, it has been established that the layers crystallize in the metastable orthorhombic phase and the epitaxial relations at the NiF₂/CaF₂ heterointerface have been determined: $ (100)_{NiF_2 } ||(111)_{CaF_2 } ,[001]_{NiF_2 } ||[1\bar 10]_{CaF_2 } $ .     

Study by electrical conductivity and infrared spectrometry of the thermal stability of defective iron spinels with aluminium and chromium

Precipitation in defective chromium- or aluminium-substituted magnetites, \(\gamma - \left( {Fe_{\left( {8/3} \right) - \left( {8/9} \right)x}^{3 + } M_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \left( {M^{3 + } = Al^{3 + } ,Cr^{3 + } ;0< x< 2} \right)\) , and defective iron aluminium chromium spinels, \(\gamma - \left( {Fe_{8/9}^{3 + } Al_{\left( {8/9} \right)\left( {2 - x} \right)}^{3 + } Cr_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \) has been investigated by electrical conductivity and infrared spectrometry in the temperature range 600 to 1200° C. For highly γ-AI-substituted magnetites and γ-iron aluminium chromium spinels the transformation of the spinel lattice into an α-rhombohedral lattice has been found to be preceded by the formation of an intermediate phase at about 900° C with a high alumina content, approximately identical to disordered γ-Al₂O₃. It is only at higher temperatures (> 1100° C) that the formation of an α-rhombohedral phase is observed. In the case of γ-Cr-substituted magnetites, temperatures of only about 700° C are required for the transformation γ → α.     

Subsurface deformation and microcrack formation in Ti–35Nb–8Zr–5Ta–O(x) during reciprocating sliding wear

The relationship between dry sliding reciprocating wear, subsurface deformation and microcrack formation in Ti–35Nb–8Zr–5Ta–O(x) has been investigated. Three subsurface zones: a chemically altered tribo-layer, a plastic shear zone, and a plastic deformation zone layer were identified, their depth increasing with increasing contact stress. Transmission electron microscopy showed {110} and {112} planar slip deformation throughout the plastic zones, the planar slip band spacing decreasing with decreasing distance to the reciprocating sliding wear surface. Within the plastic shear zone {110}/{110} and {110}/{112} slip band intersections were observed, their number density increasing with decreasing distance from the wear surface. These slip bands intersections were associated with localized shear displacement, the magnitude of the shear displacement increasing with increasing oxygen. Finally as the tribo-layer was approached microcrack formation at intersecting slip band was observed. Microcrack propagation proceeded along the interface of the {110} slip bands with microcrack linkage being observed as reorientation of the slip bands occurred. Ultimately a featureless surface tribo-layer containing cracks running both parallel and perpendicular to the wear was encountered. These observations are consistent with a model for debris formation that involves microcrack formation, linkage and ultimately shear type II shear delamination.     

{111} twinning structure and interfacial energy in nonstoichiometric TiCx with ordered carbon vacancies

Here we report the experimental and theoretical investigations of the {111} twinning structures in nonstoichiometric TiC_0.7 with ordered carbon vacancies. Owing to the ordering of carbon vacancies, a cubic Ti₂C-type ordered phase is formed in nonstoichiometric TiC_x (0.53 ≤ x ≤ 0.81). Via the TEM measurements, the {111}-specific twinning structure with incoherent boundary has been observed in ordered TiC_0.7. The first principles calculations indicate that the presence of ordered carbon vacancies leads to reduction in the energy of {111}_Ti type twinning interface, thus favoring the formation and stabilization of {111}_Ti-specific twinning structure in the ordered TiC_x.