Hardness anisotropy and its dependence on composition in sodium tungsten bronzes and rhenium trioxide single crystals

Hardness anisotropy measurements using a Knoop diamond indenter on {0 0 1} and {0 0 1} surfaces of Na _x WO₃ (0.4<x<0.8) and ReO₃ single crystals with the cubic perovskite structure show that hardness is determined by slip on {1 1 0} 1 1 0. Room temperature slip is produced by Knoop and Vickers microhardness indentations on polished crystals and confirms the active slip system identified from a consideration of anisotropy. The hardness anisotropy is more pronounced as the sodium content of the crystals increases. The data suggests that hardness of Na _x WO₃ is dependent on both plane and direction.     

Evaluation of microstructures associated with hardness indentations in InP

Microstructures associated with Knoop indentations on the (001) and (011) planes of single crystals of InP were evaluated_by transmission electron microscopy (TEM). The results show that different {111} 1¯1 0 slip systems are activated depending on the crystallographic direction along which the long axis of Knoop indentor is aligned. A simple explanation is developed which makes it possible to rationalize the observed slip systems and the hardness anisotropy of InP.     

Knoop microhardness measurements on lithium niobate and lithium tantalate

Knoop microhardness measurements were made on the (11.0), (01.0) and (00.1) planes of the trigonal isostructural compounds lithium niobate and lithium tantalate. The data indicate uniform hardness in the 〈11.0〉 and 〈01.0〉 directions and greater hardness in the [00.1] direction. In accordance with previous findings of hardness anisotropy in materials with hexagonal crystal structure, the present data indicate preferred slip on basal planes. The ratio of hardness to the shear modulus C ₆₆ is close to 0.1, which is usually found in covalent-bonded solids.     

Some aspects of the static and dynamic compressive behaviour of β-brass single crystals

The compressive behaviour of β-brass single crystals has been investigated in uninterrupted static and dynamic tests and in interrupted tests using static-static, static-dynamic, dynamic-dynamic and dynamic-static loading sequences. Static and dynamic strain-rates were 1.5×10^?4 and 3.2×10³ sec^?1 respectively. Slip traces on the statically deformed crystals were wavy and deformation occurred by single slip on either (ī01) [111] or (¯211) [111] or by a transition mode involving both (ī01) [111] and (¯211 [111]. Except for anomalous behaviour in the dynamic reload following static preload the dynamic slip traces were straight with deformation occurring by multiple slip on four {110} planes involving two 〈111〉 directions. It is shown that there is no direct causal relationship between the lower work-hardening rate and level of flow stress and the crystallography of slip in dynamic deformation. The work-hardening rate and flow stress in static and dynamic loading are rather determined by the dynamics of the deformation. The differences in the substructural features as observed by transmission electron microscopy arise principally from the differences in the slip modes and cannot be interpreted as controlling the stress-strain behaviour. The low work-hardening rate and flow stress in dynamic deformation is believed to be due to the production of short-lived disorder. The absence of a/2〈111〉 dislocations in thin foils is explained in terms of the fast reordering reaction in β-brass.     

Microdurete de monocristaux d'alumines β

Knoop microhardness is investigated as a function of indenter orientation on the {112?0} and (0001) planes of β_M+ alumina single crystals (M⁺ = Na⁺, Ag⁺, K⁺, Tl⁺, NH₄⁺). For the prismatic planes maximum hardness values are always obtained along the |0001| direction. For the basal plane the direction corresponding to the maximum hardness depends upon the nature of the M⁺ ion. For β_Na alumina the maximum hardness value is found along the 〈112?0〉 directions; in this case microhardness anisotropy analysis suggests that the active slip systems are (0001) 〈112?0〉. For β_Ag, β_K, β_Tl, the maximum hardness value is along the 〈101?0〉 directions. This difference of mechanical behaviour might be in relation with the structural differences in these β aluminas (variations in the local structure of the conduction planes). Temperature dependence of the microhardness for β_Na and β_Ag single crystals is reported between 20° and 700°C.     

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.     

Plastic material parameters and plastic anisotropy of tungsten single crystal: a spherical micro-indentation study

Enhancement of toughness is currently a critical engineering issue in tungsten metallurgy. The inherent toughness of tungsten single crystals is closely related to the capacity for local plastic slip. In this study we have investigated the plastic behavior of tungsten single crystals by means of micro-indentation experiments performed on specimens exposing (100), (110), and (111) surfaces. In parallel, FEM simulations were carried out with the Peirce–Asaro–Needleman crystal plasticity model considering both {110} 〈111〉 and {112} 〈111〉 slip systems. Plastic material parameters were identified by comparing the measured and predicted load–displacement curves as well as pile-up profiles. It is found that both measured and simulated plastic pile-up patterns on the indented surfaces exhibit significant anisotropy and orientation dependence, although the measured and simulated load–displacement curves manifest no such orientation dependence. The height and extension of pile-ups differ strongly as a function of surface orientation. The FEM simulations are able to reproduce the observed features of spherical indentation both qualitatively and quantitatively.     

Structure and properties of tantalum carbide crystals

Single crystals of tantalum carbide, up to 2 mm in size have been grown from solution in a bath of molten iron. The slip plane was found to be {111} using a two-surface analysis on etch-pitted crystals deformed by microindentation at room temperature. Observations of etch-pit patterns around inclusions suggest that slip occurs on other planes at elevated temperatures. Maximum microhardness values between 3800 and 5200 Knoop (100 gm load) were found at a composition TaC_0.83±0.01. In regions of crystals with a carbon content less than TaC_0.83 a phase transformation was seen close to microhardness indentations in samples decarburised below 2200† C. The mechanical behaviour of tantalum carbide is discussed with reference to a general model for the electronic structure of carbides.     

Textures of tantalum metal sheets by neutron diffraction

The orientation distributions of six tantalum samples, TaPA, TaG1, TaG2, TaQ2-S1, TaQ2-S2 and TaQ2-S4, were studied by neutron diffraction and ODF analysis. The TaPA specimen is a commercial tantalum sheet with an unknown fabrication history. The TaG1 and TaG2 were fabricated from a powder metallurgical ingot by uniaxial compression, and the TaQ2 type samples were fabricated from commercial stock by similar uniaxial forging. TaQ2-S1 is the section closest to the centre of the forged disc, S2 is the intermediate section, and S4 is the section adjacent to the periphery. The texture of TaPA consisted of many components, including {014}〈100〉, {111}〈ˉ321〉, {100}〈010〉, and [111]/[100] double-fibre textures with the fibre axes oriented parallel to the normal direction. The two TaG-type specimens were dominated by the [111]/[100] double-fibre texture, accompanied by a weak {100}〈010〉 cube texture. The three sections of TaQ2 had much higher degrees of texture than the TaG-type samples, with an extremely strong (111) peak, which consists of (111)〈11ˉ2〉, (111) 〈ˉ1ˉ12〉, and [111] fibre texture. The average pole density of the three equivalent orientations of (111)〈11ˉ2〉 was the strongest for the S1 with over 150 multiples of random distribution (mrd), and gradually decreased with increasing radial distance to about 100 mrd for the S4 section. On the other hand, the average intensity of (111)〈ˉ1ˉ12〉 type orientations was increased from about 40 mrd at S1 to about 100 mrd for the S4 section.     

Solidification of tin droplets embedded in an aluminium matrix

The solidification behaviour of tin droplets embedded in an aluminium matrix in a rapidly solidified Al-5 wt % Sn alloy has been investigated by a combination of transmission electron microscopy and differential scanning calorimetry. Detailed transmission electron microscopy shows that rapidly solidified Al-5 wt % Sn consists of about 5 μm diameter columnar aluminium grains, with a fine-scale distribution of 20–300 nm sized tin particles embedded within the aluminium grains, and 100–400 nm sized tin particles at the aluminium grain boundaries. The tin particles exhibit two different orientation relationships with the aluminium matrix and a variety of different faceted shapes: {1 1 1}_Al∥{1 0 0}_Sn and 〈¯2 1 1〉_Al∥〈0 1 0〉_Sn, with the main facet parallel to {1 1 1}_Al, and {1 0 0}_Sn; and {1 0 0}_Al∥{1 0 0}_Sn and 〈0 1 1〉_Al∥〈0 1 1〉_Sn, with the main facet parallel to {1 0 0}_Al and {1 0 0}_Sn.In situ heating in the transmission electron microscope shows that the different tin particle shapes are not affected by heat treatment in the solid state, but change into a truncated octahedral shape bounded by {1 1 1}_Al and {1 0 0}_Al facets when the tin particles melt. The {1 0 0}_Al-liquid Sn interfacial energy is about 9% larger than the {1 1 1}_Al-liquid Sn interfacial energy just above the tin particle melting point, and the {1 0 0}_Al/{1 1 1}_Al interfacial energy anisotropy decreases gradually as the temperature increases above the melting point. Differential scanning calorimeter experiments show that the liquid tin droplets solidify in three stages. Firstly, the larger tin droplets at the aluminium grain boundaries solidify by nucleation on catalytic trace impurities, over a temperature range of 170–140 °C. Secondly and thirdly, the smaller tin particles embedded within the aluminium grains solidify by catalytic nucleation on the {1 0 0}_Al and {1 1 1}_Al facets, over the two temperature ranges of 140–128 °C and 128-115°C. Catalytic nucleation of the solidification of tin takes place at special sites such as steps or dislocations on the {1 0 0}_Al and {1 1 1}_Al facets with contact angles of 55° and 59°.     

Hardness anisotropy of SrF2, BaF2, NaCl and AgCl crystals

The value of Knoop microhardness was obtained for crystals of SrF₂, BaF₂, NaCl and AgCl by indentation in various directions on several crystallographic planes. In all cases, the hardness is essentially dependent on the crystallographic direction along the long axis of the indentor and independent of the plane of indentation, as first reported by Garfinkle and Garlick for other cubic crystals. In addition, although the absolute value of hardness varies from one crystal to another, the hardness anisotropy was quite similar for all crystals. Since the primary slip mode is different among the crystals tested, it is concluded that hardness anisotropy cannot be used to determine the primary slip mode.     

Morphology of C60 Crystals Grown from the Vapor Phase

Abstract

The morphology of C₆₀ crystals grown from the vapor phase have been studied. In all observations, only hexagonal and rectangular shaped crystal faces were found. Very different morphology, highly faceted {111} faces and flat {100} faces were observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). the highly regular shape and similar distance between all neighboring macrosteps observed for the {111} faces can be explained by taking into account that edges of two adjacent {111} and {100} planes can act as step sources.     

Plastic flow and fracture of tantalum carbide and hafnium carbide at low temperatures

Knoop and Vickers hardness measurements have been made on tantalum carbide and hafnium carbide single crystals. The hardness varies with orientation of the indenter in the crystal, but indentations in the two carbides are of very different character, TaC behaves in a relatively ductile manner and deforms plastically before cracking, while HfC exhibits extremely limited plastic flow and cracks on indentation. Moreover, the preferred slip plane is {111} in TaC but is {110} in HfC. These results are related to the reported physical properties of these carbides. In particular, the observed mechanical behaviour of TaC appears to be consistent with the more metallic nature of this carbide.     

Evolution of the spread of crystal orientation with plastic deformation in a cold-rolled Cu single crystal

Using scanning electron microscopy, we investigated how the microstructure of a Cu single crystal with a {15 12 9}〈9 10 3〉 orientation evolved from cold rolling. The first 50 % rolling caused its crystal orientation to rotate to {211}〈111〉. Although orientation splitting occurred near the surface of the single crystal, band-like regions with near-{211}〈111〉 orientations were still present after the fourth 50 % rolling. We measured the spread of crystal orientation in the near-{211}〈111〉 regions as a function of the total plastic equivalent strain induced by all rolling steps. When 50 % rolling was performed less than twice, the spread of crystal orientation was proportional to the square root of the plastic equivalent strain. Based on our results, we discussed the relationship between the spread of crystal orientation and the plastic equivalent strain generated by rolling.     

The orientation and morphology of chromium deposits on hot Cu{111} substrates

Chromium (1.5–20 nm thick) was vapour deposited in ultrahigh vacuum (2×10^-9 Torr) onto single-crystal Cu{111} films. The copper substrate temperatures T_s were in the range 75–256 °C. Transmission electron microscopy and electron diffraction were used to study the orientation and morphology of the deposits. For T_s ≲ °C the electron diffraction patterns showed arced chromium reflections consistent with a distribution of orientations between Nishiyama- Wassermann (NW) and Kurdjumov-Sachs (KS) at ±5° 16′ from NW. A greater tendency towards KS was observed as T_s increased to about 130 °C. For T_s = 190 and 256 °C relatively well-defined KS orientations occured. These results are interpreted in terms of various geometric models of f.c.c.-b.c.c. interfaces. At T_s ≲ 85 °C the morphology was qualitatively similar to that observed for room temperature substrates: flat irregularly shaped crystals within which a substructure of parallel-oriented crystallites with elongated shape existed. For T_s ≲ 130 °C the morphology changed from the flat irregularly shaped crystals to isolated three- dimensional crystals with an elongated shape. The long direction of the crystals was approximately parallel to the direction of least misfit, i.e. Cr〈111〉  Cu〈110〉.     

Annealing twins in a multifunctional beta Ti-Nb-Ta-Zr-O alloy

The grain boundary character distribution and annealing twins in a multifunctional β-type Ti-23Nb-0·7Ta-2Zr-O alloy having a stable bcc phase structure are investigated by electron backscattering diffraction (EBSD). The results show that the coincident site lattice (CSL) boundaries, including Σ3 and Σ11 twin boundaries mainly form at the early stage of recrystallization. {112}〈111〉 and {332} 〈113〉 annealing twins are observed to occur in the completely recrystallized Ti-23Nb-0·7Ta-2Zr-O alloy.     

Microplasticity at room temperature of single-crystal titanium carbide with different stoichiometry

Single crystals of titanium carbide with a C-to-Ti range of 0.64 to 0.99 were plastically deformed at room temperature with a hardness indenter and a drill. The operating slip systems were determined by hardness anisotropy and transmission electron microscopy. The results were characteristic for bulk material deformation of TiC, below, as well as above, the brittle-to-ductile transition temperature. A typical low temperature behaviour is the formation of cracks and dislocation motion along the slip systems {1 1 0} 〈1 1 0〉 and {1 0 0} 〈1 1 0〉, which are both common in the rock-salt structure. The high temperature deformation is characterized by the slip system {1 1 1} 〈1 1 0〉. The degree of plastic deformation and the importance of the slip system {1 1 1} 〈1 1 0〉 increases as the C-to-Ti ratio decreases from 0.99 to 0.64.     

Epitaxial growth of CoSi2 on Si(001) by reactive deposition epitaxy: Island growth and coalescence

Epitaxial CoSi₂ layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi₂(001) follows the Volmer-Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t_Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi₂/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)_CoSi2||(001)_Si and [100]_CoSi2||[100]_Si. Platelet-shaped CoSi₂ islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)_CoSi2||{111}_Si) and their narrow 〈110〉 directions by {511}_CoSi2||{111}_Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}_CoSi2||(001)_Si, and {1¯1¯1}, with {1¯1¯1}_CoSi2||{11¯1}_Si, respectively. The early stages of film growth (t_Co ≤ 13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2 × 1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t_Co ≥ 13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi₂(001) layer, with a twin density of 2.8 × 10¹⁰ cm^− 2, is obtained at t_Co = 50 Å.     

P、Ti对高强IF钢{=111}面织构的影响

借助电子背散射衍射（EBSD）技术测量和计算了高强IF钢退火试样的取向分布函数（ODF）、织构组分的含量和7取向线强度。研究了{111}（112）和{111}010）织构组分的变化,分析了P、Ti对{111}面织构的影响机理。P的存在阻碍了位错的运动和晶界的迁移,进而使再结晶晶粒取向趋于一致,形成较尖锐的{111}面织...     

Modeling of large plastic deformation behavior and anisotropy evolution in cold rolled bcc steels using the viscoplastic ?-model-based grain-interaction

In this paper, a micromechanical approach is used to predict the mechanical response and anisotropy evolution in BCC metals. Particularly, cold rolling textures and the corresponding yield surfaces are simulated using the newly developed viscoplastic intermediate ?-model. This model takes into account the grain interactions but without the Eshelby theory. In this work, we compare our results to those predicted by the upper and lower bounds (Taylor and Static) as well as those of the viscoplastic self-consistent (VPSC) model. The results are compared in terms of predicted slip activity, texture evolution and yield loci. For the simulations, we considered two cases: the restricted slip, {1 1 0}〈1 1 1〉, and the pencil glide, {1 1 0}〈1 1 1〉 + {1 1 2}〈1 1 1〉 + {1 2 3}〈1 1 1〉. In addition, we present a qualitative comparison with experimental cold rolling textures taken from the literature for several BCC metals: electrical, ferritic, Interstitial-Free (IF) and low carbon steels. Our results show that the pencil glide assumption is adequate for low carbon and IF-steels and that the restricted slip assumption is well suited for ferritic and electrical steels.