Formation of crystallographic texture in titanium nickelide single crystals during rolling

The texture formation in the single crystals of the Ti-48 at % Ni-2 at % Fe alloy rolled at a temperature of 350°C up to a strain of 80% in eleven different initial orientations is examined. There are three stable initial orientations that remain unchanged in rolling: {011}〈011〉, {111}〈011〉, and {111}〈112〉. The TiNi single crystals are shown to be deformed by means of a combined action of slip in systems {011}〈001〉 and twinning in systems {114}〈221〉 and {118}〈441〉. The types of formed rolling texture in the single crystals depend on their initial orientation and strain.     

Effect of plastic anisotropy on the creep strength of single crystals of a nickel-based superalloy

The effect of plastic anisotropy, which is caused by the arrangement of slip systems, on the creep strength of notched specimens of Ni-based superalloy single crystals, is described. It was revealed that the creep strength of the notched specimens was affected by the crystallographic orientation, not only in the tensile direction, but also in the thickness direction. The creep strength was superior in the notched specimen with the [011] tensile and [100] plate-normal orientation, whereas the notched specimen with [011] tensile and [100] plate-normal orientation exhibited extremely poor creep strength. In the case of specimens whose tensile orientation was [011], results of the creep-rupture tests at 973 K were in agreement with the assumption of the operation of {111}〈112〉 slip systems. The creep strength in the notched specimen with [001] tensile and [100] plate-normal orientations was superior to that in the notched specimen with [001] tensile and [011] plate-normal orientations. When the tensile orientation was [001], the results of the creep-rupture tests were in agreement with the assumption of the operation of {111}〈112〉 slip systems during primary creep region and {111}〈101〉 slip systems during secondary creep region.     

The creep-damage constitutive and life predictive model for nickel-base single-crystal superalloys

A two-state-variable creep-damage constitutive and life predictive model that has been built is discussed in this article. The cavitation-controlled damage mechanism and microstructural deg-radation, i.e., material damage mechanism, are considered. The latter is derived mainly from the rafting and derafting of the precipitate γ′. The model has been verified by the creep ex-periments of nickel-base single-crystal DD3 at 760 °C and 850 °C. The steady creep and tertiary creep can be predicted satisfactorily. The active slip systems are confirmed as octahedral 〈112〉 {111} based on the lattice rotation. The parameter C reflecting material damage mechanism depends on the crystallographic orientation and can be assigned to the value C _〈001〉 ^α along 〈001〉 crystallographic orientation and C _〈011〉 ^α along 〈011〉 orientation partially. The life in different crystallographic orientations can be predicted satisfactorily.     

Structure–phase characteristics and the mechanical properties of single-crystal nickel-based rhenium-containing superalloys with carbide–intermetallic hardening

Single crystals of rhenium-containing ZhS32-VI, ZhS32U nickel superalloys with the 〈001〉, 〈011〉, and 〈111〉 crystallographic orientations have been produced by directional solidification. The alloying element segregations and the thermal stability of the microstructure consisting of a γ solid solution and hardened by precipitates of the γ′ phase and MC carbides are studied. The crystal lattice parameters of the γ′ and γ phases; the γ/γ′ misfit; and the liquidus, solidus, and γ′-solvus temperatures of the alloys have been found. The temperature dependence of the γ′-phase solubility has beeisn determined. The temperature–orientation dependences of the tensile strength characteristics in the range 20–1150°C and the low-cycle fatigue at 850°C of the alloy single crystals with the 〈001〉, 〈011〉, and 〈111〉 orientations are presented.     

DD15单晶高温合金持久性能各向异性

研究了[001]、[011]和[111]3种不同取向的DD15单晶高温合金的热处理组织、980 ℃/300 MPa和1 150℃/120MPa的持久性能、持久断口和断裂组织.结果表明在与定向凝固方向垂直的截面上,3种取向合金具有明显不同的热处理组织形貌,γ'相的形状分别为规则的正方形、矩形和多边形.合金在980℃/30...     

Microstructure Evolution and Analysis of A [011] Orientation, Single-Crystal, Nickel-Based Superalloy During Tensile Creep

By means of the elastic?Cplastic finite-element method (FEM) for calculating the distribution features of the von Mises stress and strain energy density, the influences of the applied stress on the von Mises stress of the ????/?? phases and the rafting of the ???? phase for the [011] orientation, single-crystal, nickel-based superalloy are investigated. The results show that, after being fully heat treated, the microstructure of the [011] orientation, single-crystal, nickel-based superalloy consists of the cuboidal ???? phase embedded coherently in the ?? matrix, and the cuboidal ???? phase on (100) plane is regularly arranged along a 45?deg angle relative to the [011] orientation. Compared with the matrix channel of [010] orientation, the bigger von Mises stress is produced within the [001] matrix channel when the tensile stress is applied along the [011] orientation. Under the action of the larger principal stress component, the bigger expanding lattice strain occurs on the (001) plane of the cuboidal ???? phase along the [010] direction, which may trap the Al, Ti atoms with a bigger atomic radius for promoting the directional growth of the ???? phase into the stripe-like rafted structure along the [001] orientation. The changes of the interatomic potential energy, misfit stress, and interfacial energy during the tensile creep are thought to be the driving forces of promoting the elements?? diffusion and directional growth of the ???? phase.     

The effects of orientation and thickness on the notch-tensile creep strength of single crystals of a nickel-base superalloy

The effects of crystallographic orientation and thickness of specimen on the notch-tensile creep strength of single crystals of a nickel-base superalloy UDIMET∗520 has been examined at 700°, 850°, and 900 °C. It was found that the notch-tensile creep strength of thin specimens depended on the crystallographic orientations not only in the tensile direction but also in the normal direction of the specimens, and that the creep strength was superior in the thin specimens with the [011] tensile and the [011] normal orientations or the [001] tensile and the [110] normal orientations. The thick-notched specimens exhibited great creep resistance regardless of the crystallographic orientations. Formerly Graduate Student Formerly Graduate Student, Tokyo Metropolitan University     

DD407单晶高温合金760℃拉伸性能的各向异性

研究了具有[001]、[011]和[111]取向以及[001]附近取向的DD407单晶高温合金经过热处理后,在760℃温度下的拉伸性能。结果表明,该合金具有明显的拉伸性能各向异性：[001]取向上表现出了最高的屈服强度和抗拉强度;当取向逐渐偏离[001]时,强度开始降低,但在相同的偏离角度内,偏向[111]取向的试样具...     

不同析出状态下Al合金的形变及再结晶织构

The deformation and recrystallization textures of 6111 Al alloy with various precipitation states have been investigated by means of the orientation distribution functions ( ODFs ). It was found that the precipitation state had significant effects on both rolling and recrystallization textures of Al alloy. For the alloy with no or little precipitate, the orientation intensities were distributed more homogeneously along the β-fiber.With increasing aging temperature, the orientation intensities along the β-fiber increased firstly and decreased then. Simultaneity, the orientation intensities along the β-fiber were distributed more and more inhomogeneously. On the other hand, with the precipitates increasing the recrystallization textures changed gradually from {001} and very weak {011} <111> orientation to the strong {001} <311> and {011}< 111 > orientation.     

The influence of crystallographic orientation and strain rate on the high-temperature low-cyclic fatigue property of a nickel-base single-crystal superalloy

Fully reversed low-cyclic fatigue (LCF) tests were conducted on [001], [012], [-112], [011], and [-114] oriented single crystals of nickel-based superalloy DD3 with different cyclic strain rates at 950°C. The cyclic strain rates were chosen as 1.0×10⁻², 1.33×10⁻³ and 0.33×10⁻³ s⁻¹. The octahedral slip systems were confirmed to be activated on all the specimens. The experimental result shows that the fatigue behavior depends on the crystallographic orientation and cyclic strain rate. Except [001] orientation specimens, it is found from the scanning electron microscopy (SEM) examination that there are typical fatigue striations on the fracture surfaces. These fatigue striations are made up of cracks. The width of the fatigue striations depends on the crystallographic orientation and varies with the total strain range. A simple linear relationship exists between the width and total shear strain range modified by an orientation and strain rate parameter. The nonconformity to the Schmid law of tensile/compressive flow stress and plastic behavior existed at 950°C, and an orientation and strain rate modified Lall-Chin-Pope (LCP) model was derived for the nonconformity. The influence of crystallographic orientation and cyclic strain rate on the LCF behavior can be predicted satisfactorily by the model. In terms of an orientation and strain rate modified total strain range, a model for fatigue life was proposed and used successfully to correlate the fatigue lives studied in this article.     

Deformation behavior of long-range ordered AgMg

The deformation behavior of long-range ordered AgMg single crystals was investigated in tension and compression for several orientations and temperatures. The study revealed that AgMg exhibits a complex and asymmetric deformation behavior corresponding to the operation of two different primary slip vectors, <111> and <001>, whose activation depends on the crystallographic orientation and sense of the applied uniaxial stress and on temperature. Crystals of various orientations deformed between 20° and 298°K exhibited six different operative slip systems, {112} <111>, {123} <111>, {110} <111>, {120} <001>, {100} <001>, and {110} <001>. It is shown that the high strain-hardening rate exhibited by polycrystalline AgMg does not arise from the Vidoz-Brown⁵ mechanism of formation of antiphase boundary (APB) tubes on jogged superdislocations, but is associated with the operation of the {hko} <001> slip systems.     

Elevated-temperature fatigue crack growth

The fatigue crack growth behavior of MAR-M200 single crystals was examined at 982 °C. Using tubular specimens, fatigue crack growth rates were determined as functions of crystallographic orientation and the stress state by varying the applied shear stress range-to-normal stress range ratio. Neither crystallographic orientation nor stress state was found to have a significant effect on crack growth rate when correlated with an effective ΔK which accounted for mixed-mode loading and elastic anisotropy. For both uniaxial and multiaxial fatigue, crack growth generally occurred normal to the principal stress direction and in a direction along which ΔK _II vanished. Consequently, the effective ΔK was reduced to ΔK_I and the rate of propagation was controlled by ΔK _I only. The through-thickness fatigue cracks were generally noncrystallographic with fracture surfaces exhibiting striations in the [010], [011], and [111] crystals, but striation-covered ridges in the [211] specimen. These fracture modes are contrasted to crystallographic cracking along slip bands observed at ambient temperature. The difference in cracking behavior at 25 and 982 °C is explained on the basis of the propensity for homogeneous, multiple slip at the crack tip at 982 °C. The overall fracture mechanism is discussed in conjunction with Koss and Chan’s coplanar slip model.     

Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy

In this study, the TMF stress relaxation and creep behavior at 1023 K and 1223 K (750 °C and 950 °C) have been investigated for a Ni-based single-crystal superalloy. Specimens with three different crystal orientations along their axes were tested; 〈001〉, 〈011〉, and 〈111〉, respectively. A highly anisotropic behavior during TMF stress relaxation was found where the 〈111〉 direction significantly shows the worst properties of all directions. The TMF stress relaxation tests were performed in both tension and compression and the results indicate a clear tension/compression asymmetry for all directions where the greatest asymmetry was observed for the 〈001〉 direction at 1023 K (750 °C); here the creep rate was ten times higher in compression than tension. This study also shows that TMF cycling seems to influence the creep rate during stress relaxation temporarily, but after some time it decreases again and adapts to the pre-unloading creep rate. Creep rates from the TMF stress relaxation tests are also compared to conventional constant load creep rates and a good agreement is found.     

Fatigue crack propagation in Ni-base superalloy single crystals under multiaxial cyclic loads

The effects of crystallographic orientation and stress state on the multiaxial fatigue behavior of MAR-M200* single crystals were examined. Using notched tubular specimens subjected to combined tension/torsion cyclic loads, crack growth rates were determined at ambient temperature as functions of stress intensity range, the shear stress range-to-normal stress range ratio, and crystallographic orientation. Comparison of crack growth data at the same effective ΔK reveals a weak dependence of the crack growth rate on both the tube axis and the notch orientation. For a given set of tube axis and notch orientation, the crack growth rate might or might not vary with the applied stress state, depending on whether roughness-induced crack closure is present. In most cases, subcritical cracking occurs either along a single 111 slip plane or on ridges formed with two 111 slip planes. Neither fracture mode is altered by a change in the applied stress state. This complex crack growth behavior will be discussed in terms of the crack-tip stress field, slip morphology, and crack closure. Formerly with Southwest Research Institute     

Role of Different Kinds of Boundaries Against Cleavage Crack Propagation in Low-Temperature Embrittlement of Low-Carbon Martensitic Steel

The present paper investigated the relationship between low-temperature embrittlement and microstructure of lath martensite in a low-carbon steel from both microstructural and crystallographic points of view. The fracture surface of the specimen after the miniaturized Charpy impact test at 98 K (?175 °C) mainly consisted of cleavage fracture facets parallel to crystallographic {001} planes of martensite. Through the crystallographic orientation analysis of micro-crack propagation, we found that the boundaries which separated different martensite variants having large misorientation angles of {001} cleavage planes could inhibit crack propagation. It was then concluded that the size of the aggregations of martensite variants belonging to the same Bain deformation group could control the low-temperature embrittlement of martensitic steels.     

Microstructural properties of Nb-Si alloys investigated using EBSD at large and small scale

Texture and crystallographic orientation relationships in arc-melted hypoeutectic and hypereutectic binary Nb-Si alloys are investigated. Electron backscattered diffraction (EBSD) is used here in conventional conditions, i.e., at relatively high spatial resolution (<1 μm) for ∼400×400 μm fields, as well as on very large fields (1.1×1.1 mm), at lower resolution, to get a statistical overview of the microstructure. In as-cast Nb-16Si and Nb-22Si alloys (compositions are in at. pct), [001]_Nb3Si is found parallel to the local thermal gradient, with Nb₃Si + Nb eutectic cells, giving rise to a microstructure similar to that obtained by directional solidification. In Nb-22Si alloy, the following orientation relationships between poles of metallic and silicide phases have been found: (111)_Nb//(111)_Nb3Si (as cast), (011)_Nb//(011) _α-Nb5Si3, and (111)_Nb//(100) _α-Nb5Si3 (heat treated at 1500 °C, 75 hours). This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

Plastic deformation of CVD textured tungsten—I. Constitutive response

The constitutive response of CVD textured tungsten in 〈001〉, 〈011〉 and random orientations under uniaxial compression subjected to a range of strain rates is investigated. Both 〈001〉 and 〈011〉 textured specimens revealed a strong strain rate sensitivity. The 〈001〉 specimens showed large ductility at all strain rates and significant strain softening during high strain rate deformation. The 〈011〉 texture undergoes homogenous deformation under quasi-static loading but failed prematurely due to extensive grain boundary cracking during high strain rate loading. The random orientation specimens exhibited brittle failure. The temperature rise during high strain rate deformation was measured using high speed infrared detectors. A physically based crystal plasticity model motivated by dislocation reactions in b.c.c. metals is outlined. The model predicts the dependence of constitutive response on the texture in tungsten polycrystals and suggests that the transverse tensile stresses which develop in 〈011〉 orientation due to the crystallographic asymmetry could be responsible for observed grain boundary cracking.     

Effect of hot rolling on the dendritic texture of directionally solidified steel ingots

Directionally solidified ingots of three commercial steels—AISI 1010, Fe-3.4 pct Si, and Type 430 stainless steel—were hot-rolled at 1850°F in order to study the effect of hot deformation on the as-cast dendritic texture. The strong dendritic (100) orientation of both the Fe?Si and Type 430 alloys was completely destroyed by the heavy reductions typical of the commercial hot rolling of ingots. The primary effect of hot rolling is to eliminate the texture present in the ingot, and to create certain new textures. These new textures are in every case weak. For example, the AISI 1010 steel, which had very little of the dendritic <100> orientation in the ingot stage, has a combination of two weak textures after hot rolling: (100) [011] and (110) [110]. Likewise, with the other two materials, which had a strong dendritic <100> orientation in the ingot stage, hot rolling resulted in weak textures: (110) [001] with a rotation of this orientation of ±45 deg about the [001] rolling direction, followed by (110) [001] rotated ±35 deg about the [110] in the transverse direction.     

On the primary creep of CMSX-4 superalloy single crystals

The effect of orientation on the primary-creep mechanism of the Ni-based single-crystal superalloy CMSX-4 is examined. Four specimens with orientations within 20 deg of the [001] axis are deformed at 750 °C and 750 MPa and show a decreasing amount of primary creep as the tensile axis approaches the [001]–[011] symmetry boundary. Of these, specimen N lies within 1 deg of [013] and shows a negligible primary creep and a very low secondary creep rate. For this specimen, direct observation in the transmission electron microscope (TEM) and analysis of the shape change show that 〈112〉{111}, stacking-fault shear, is absent. Analysis of the dislocations present in the gamma precipitates and at the γ/γ′ interface shows that the only dislocations present have the Burgers vectors a/2[101] and a/2[10-1], which cannot combine to nucleate the dislocations necessary for stacking-fault shear. Thus, it is argued that the reason for the low degree of primary creep for orientations close to the [001]–[011] symmetry boundary is not the interaction between two equally stressed 〈112〉{111} systems, but the lack of either. As the orientation moves away from the [001]–[011] boundary, the range of dislocation Burgers vectors increases and stacking-fault shear is nucleated; the amount of primary creep increases as a consequence.     

Assessment of Plastic Deformation Induced by Indentation on a Large Grain on Inconel 600 Using Synchrotron Polychromatic X-ray Microdiffraction

A synchrotron-based three-dimensional (3-D) Laue technique called Differential Aperture X-ray microscopy (DAXM) was used to investigate plastic deformation of Inconel 600 induced by indentation. The DAXM technique is capable of probing up to 60 to 100 ??m into the Ni alloy, with micron resolution. A conical indenter was used to generate an indent on a large surface grain on Inconel 600. The DAXM Laue images from the uppermost grain exhibited pronounced streaking and splitting of Laue spots, which increased as the grain boundary was approached. Splitting of the Laue patterns correlates with subgrain or dislocation cell formation. A significant amount of dislocation cell formation was found within the 1-??m voxels probed by DAXM. A change in total angle of 8.79 deg was determined for the uppermost grain from the diffraction data from depths 4 to 28 ??m, with an average misorientation angle of 2.15 deg between the dislocation cells. The next grain having a different crystallographic orientation continued to rotate in the same direction as the uppermost grain due to the large plastic deformation.