Initial Stage Of Plastic Deformation Research Articles

Pyramidal dislocation driven martensitic nucleation: A step toward consilience of deformation scenario in fcc materials (II)

Dislocation glides and their interactions with other defects are central to our understanding of deformation mechanism enhancing plasticity and damage tolerance. Martensitic transformation (MT) is a fascinating phenomenon overcoming strength-elongation trade-off and thus tailoring structure-property architecture. However, dislocation plasticity of Fe-based hexagonal close-packed (hcp) martensite is still challenging due to its metastability, further complicated by controversies surrounding pyramidal dislocation even in pure hcp metals. To resolve the uncertainties, we address the pyramidal-dislocation-driven plasticity in Fe-based hcp martensite by employing in-situ transmission electron microscopy (TEM) and high-resolution (HR) annular bright field (ABF) imaging together with dislocation-contrast analyses. We show that the activation and dissociation of pyramidal dislocation govern the initial stage of plastic deformation, while subsequent cross-slip by the cooperative motion of dissociated pyramidal dislocations plays a key role in nucleation of new hcp martensite. By incorporating current dislocation model into previous models coupled with stacking-fault-energy concept, we propose a synthesized deformation scenario that offers a comprehensive perspective on plasticity and transformability.

Void-induced mechanisms in tensile behavior of nickel-based single crystal superalloys

Void defects significantly impact the tensile properties of nickel-based single crystal superalloys. In this work, the dynamic response of void-included nickel-based single crystal superalloys under tensile loading was studied using molecular dynamics method. The effects of porosity and void size on the tensile behavior and the evolution of internal defects were explored from a microscopic perspective. The results indicate that the presence of voids promotes the development of internal dislocation defects and atomic phase transitions, especially in the initial stage of plastic deformation. The tensile strength decreases with increasing porosity. Plastic deformation and atomic phase transitions typically initiate between voids and continue until complete fracture, with shear strains and dislocation defects continuously concentrating around the voids. Notably, some HCP defect atoms distant from voids revert to FCC phase atoms during the tensile process, leading to a decrease in dislocation density. Additionally, the mode of fracture in the porous model is shear fracture, with shear strain and dislocation defects remaining at the fracture surface after complete fracture. The effects of void size on the tensile strength are relatively small. As the void size decreases, the shear strain bands in the models become more regular and the dislocation density decreases. However, the impact of small-sized voids on the material becomes increasingly evident with further stretching.

Correlation between the microstructure and deformation behavior of a PM fine-grained duplex steel

A fine-grained duplex steel with a composition of Fe–5Mn–2Al-0.6C (wt.%) was fabricated using a powder metallurgy (PM) technology of thermomechanical consolidation by hot extrusion of powder compact. The microstructure consisted of α′-martensite, residual austenite (RA), and a small amount of Al2O3 particles. Subsequent heat treatment was performed to adjust the microstructure and mechanical properties. This study focuses on the pre-and post-heat treatment microstructure of the material, elucidates the reasons for its formation, and explains how microstructural changes influence tensile deformation behavior. The results show that the heat treatment caused the precipitation of nanoscale carbide within the martensite, which significantly increased the yield strength from 792 MPa to 1078 MPa. While heat treatment altered the size and distribution of RA regions in the microstructure, the amount of RA transformed during deformation remained proportional to the flow stress in both materials, indicating that the flow stress dictates the amount of phase transformation of ultrafine grained RA. Therefore, in the heat-treated material with a higher yield strength, a larger amount of RA transformed during the initial stage of plastic deformation, leaving less RA to sustain a work-hardening rate in subsequent deformation, resulting in a decrease in ductility from 5.5 % to 3.6 % and fracture stress from 1674 to 1453 MPa. In addition, the in-situ formed Al2O3 particles facilitated grain refinement of the extruded rod, but had less effect on the microstructure and properties of the heat-treated sample. This study serves as a valuable reference for comprehending the influence of microstructural changes in PM manganese steel on tensile deformation behavior.

Tensile and High Cycle Fatigue Performance at Room and Elevated Temperatures of Laser Powder Bed Fusion Manufactured Hastelloy X.

The application potential of additive manufacturing nickel-based superalloys in aeroengines and gas turbines is extensive, and evaluating their mechanical properties is crucial for promoting the engineering application in load-bearing components. In this study, Hastelloy X alloy was prepared using the laser powder bed fusion process combined with solution heat treatment. The tensile and high cycle fatigue properties were experimentally investigated at room temperature as well as two typical elevated temperatures, 650 °C and 815 °C. It was found that, during elevated-temperature tensile deformation, the alloy exhibits significant serrated flow behavior, primarily observed during the initial stage of plastic deformation at 650 °C but occurring throughout the entire plastic deformation process at 815 °C. Notably, when deformation is small, sawtooth fluctuations are significantly higher at 815 °C compared to 650 °C. Irregular subsurface lack of fusion defects serve as primary sources for fatigue crack initiation in this alloy including both single-source and multi-source initiation mechanisms; moreover, oxidation on fracture surfaces is more prone to occur at elevated temperatures, particularly at 815 °C.

Microstructural mechanisms endowing high strength-ductility synergy in CoCrNi medium entropy alloy prepared by laser powder bed fusion

CoCrNi medium entropy alloy (MEA) exhibits significant potential as a structural component for engineering applications. However, the traditional processing methods for pursuing the superior mechanical properties of CoCrNi MEA are often time-consuming and inefficient. Laser powder bed fusion (LPBF) offers substantial processing flexibility without the need for complex secondary processing. In this study, we optimized the processing parameters for CoCrNi MEA through an orthogonal experimental design, achieving as-printed CoCrNi components with a relative density of up to 99.4 %. The microstructure of the as-printed CoCrNi revealed hierarchical features, including the molten pools, equiaxed and elongated columnar grains, sub-grain cellular microstructures, and high-density dislocation networks. The mechanical properties of as-printed CoCrNi were exceptional, demonstrating a synergistic combination of strength and ductility (yield strength: approximately 660.91 MPa, tensile strength: approximately 892.78 MPa, elongation: approximately 33.28 %, and a product of strength and elongation: 27.45 GPa %). Experimental characterization elucidated the activation and interplay of mechanisms such as dislocations, stacking faults, twinning-induced plasticity, and transformation-induced plasticity. These mechanisms collaboratively enhanced the refinement and heterogeneity of substructures, thereby endowing the as-printed CoCrNi with significant strength-ductility synergy. Molecular dynamics simulations indicated that, in the initial stages of plastic deformation, a significant activation of Shockley partial dislocations occurred, leading to the formation of stacking faults and the emergence of Hexagonal Close-Packed (HCP) phases. As plastic deformation progressed, a reverse phase transformation from HCP to Face-Centered Cubic (FCC) took place, resulting in the formation of nanotwins. This transformation generated a heterogeneous microstructure comprised of both nanotwins and HCP phases, suggesting a sequential twinning and phase transformation pathway in as-printed CoCrNi: from FCC to HCP, and subsequently to FCC nanotwins.

3D microstructural and strain evolution during the early stages of tensile deformation

Dislocation patterning and self-organization during plastic deformation are associated with work hardening, but the exact mechanisms remain elusive. This is partly because studies of the structure and local strain during the initial stages of plastic deformation are a challenge. For this reason, literature data typically cover strains from 0.05-0.1 and higher. Here we use Dark Field X-ray Microscopy to generate 3D maps of embedded 350×900×72μm3 volumes within three pure Al single crystals. Tensile deformation was applied to true strains of 0.6%, 1.7%, and 3.5% along the [10 13 −10] direction. Orientation maps revealed the existence of two distinct types of planar dislocation boundaries both at 0.6% and 1.7% but no systematic patterning. At 3.5%, these boundaries have evolved into a well-defined checkerboard pattern, characteristic of Geometrically Necessary Boundaries, GNBs. The crystallographic alignment of the GNBs match that in polycrystals for grains of similar orientation. The GNB spacing measured perpendicular to the planesis ≈6μm and the misorientation ≈0.2°, in fair agreement with literature data for higher strains. By contrast to the sharp boundaries observed at higher strains, the boundaries are associated with a sinusoidal orientation gradient, showing that they are not yet fully formed. Maps of the elastic strain along the (111) direction exhibit strain variations of ±0.0002 with an average domain size of 3μm.

Influence of Quenching and Partitioning on the Mechanical Properties of Low‐Silicon 33MnCrB5 Boron Steel

Quenching and partitioning (QP) is a heat treatment that is designed to enhance both the mechanical properties and ductility of low‐ and medium‐carbon steels. This treatment is performed on steels with a tailored chemical composition. Herein, QP treatments are designed and performed on commercial low‐silicon 33MnCrB5 boron steel. Different temperatures (evaluated using thermodynamic simulations) and times are tested. Scanning electron microscopy investigations are conducted to observe the microstructure, whereas X‐ray diffraction and electron backscattered diffraction analyses are performed to assess the presence and amount of retained austenite (RA). Tensile tests are performed to investigate the mechanical properties. The designed treatments introduce a fraction of up to 4.6% of RA in the final microstructure. Tensile tests show that the QP samples are characterized by high ultimate tensile strength (1633–1756 MPa) with an increased elongation at break with respect to the reference quenching and tempering condition (16–18% versus 9%). Hardening coefficients are linked to martensite tempering in the initial stages of plastic deformation, whereas at higher strains, they are mostly influenced by RA presence. The proposed treatments are successfully performed on 33MnCrB5 grade, leading to a set of tensile properties that are not exploitable with traditional treatments.

In situ neutron diffraction revealing the achievement of excellent combination of strength and ductility in metastable austenitic steel by grain refinement

The yield stress of Fe-24Ni-0.3C (wt%) metastable austenitic steel increased 3.5 times (158 → 551 MPa) when the average grain size decreased from 35 μm (coarse-grained [CG]) to 0.5 μm (ultrafine-grained [UFG]), whereas the tensile elongation was kept large (0.87 → 0.82). In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms. The initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip, with deformation-induced martensitic transformation (DIMT) also occurring in the later stage of deformation. Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain, which is attributed to the following effects. (i) Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the 〈111〉//LD (LD: loading direction) austenite grains, which were the most stable grains for DIMT. As a result, most of the 〈111〉//LD austenite grains in the UFG specimen failed to transform into martensite. (ii) Grain refinement also suppressed the autocatalytic effect of the martensitic transformation. Nevertheless, the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation. The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.

A comparative study on the microstructure and strengthening behaviors of Al matrix composites containing micro- and nano-sized B4C particles

Two types of Al matrix composites (AMCs) containing micro-sized B4C particles (m-B4C/Al) and nano-sized particles (n-B4C/Al) were prepared by hybrid accumulative roll-bonding. The influences of m-B4C and n-B4C particles on the microstructure and mechanical properties of the AMCs were investigated systematically. Microstructure observations showed that B4C particles were uniformly distributed in the matrix with well-bonded interfaces in both the two types of composites. The n-B4C/Al composites presented finer grain size compared to the m-B4C/Al, indicating that n-B4C particles are more effective in enhancing the grain refinement and suppressing the grain growth than m-B4C particles. While the n-B4C/Al composites exhibited higher microhardness and strength, the m-B4C/Al composites showed higher elongation. Moreover, the strain hardening rate of the n-B4C/Al composites was higher at the initial stage of plastic deformation, but lower than that of the m-B4C/Al composites at larger strain. Furthermore, nanoindentation tests showed an obvious increment of nanohardness with the increase of deformation in the m-B4C/Al composites. The different strengthening behaviors of m-B4C and n-B4C particles can be attributed to the particle-dislocation interactions at different stages of plastic deformation. This work demonstrated the significant differences between the deformation and strengthening behaviors of AMCs reinforced by micro- and nano-sized B4C particles, providing novel insights for the design of AMCs with high strength and toughness by taking advantages of the hybrid-sized reinforcement particles.

RESEARCH OF SPECIAL LIMITS DURING HEAT TREATMENT OF MATERIALS IN THE TWO-PHASE REGION UNDER SUPERCRITICAL TEMPERATURE INFLUENCE

The results of the research on establishing the dependence of the coercive force (Нs) on special boundaries in a low-carbon alloy are given. Annealing at a temperature of 900 ºС with a holding time of 1 to 3 h leads to an increase in the number of special boundaries from 22.7 to 37.17% and to an increase in magnetic permeability and, accordingly, a decrease in the coercive force from 1.60 to 1.24 A/cm. When the load is axially stretched, the coercive force changes. The initial stage of plastic deformation is most sensitive to the growth of coercive force, which allows us to identify areas in which local plastic deformation has occurred, which indicates a significant decrease in the operational characteristics of parts.

Investigations on the tensile deformation of pure Mg and Mg–15Gd alloy by in-situ X-ray synchrotron radiation and visco-plastic self-consistent modeling

In this study, the texture evolutions of two Mg materials during tension are explored. In-situ X-ray synchrotron and Visco-Plastic Self-Consistent (VPSC) modeling are employed to investigate the different deformation modes between pure Mg and Mg–15Gd (wt.%) alloy. These two materials with a strong extrusion texture show large different slip/twinning activity behaviors during tensile deformation. The basal 〈a〉 slip has the highest contribution to the initial stage of plastic deformation for pure Mg. During the subsequent plastic deformation, the prismatic slip is dominant due to the strong ED // 〈100〉 fiber texture. In contrast, the deformation behavior of Mg–15Gd alloy is more complex. Twinning and basal slip are dominant at the early stage of plastic deformation, but further deformation results in the increased activation of prismatic and pyramidal slips. In comparison to pure Mg, the ratios of the critical resolved shear stress (CRSS) between non-basal slip and basal slip of the Mg–15Gd alloy are much lower.

Dislocation behavior in initial stage of plastic deformation for CoCrNi medium entropy alloy

The effects of crystal orientation on the plastic deformation behavior for typical CoCrNi medium entropy alloy under tensile and compressive loading were investigated by molecular dynamics simulations. The Lomer-Cottrell (L-C) structure and parallel hexagonal close packed (HCP) bands are produced in the [111] and [11̅0] orientations at the initial stage of tensile deformation, respectively. However, perfect dislocations and two types of non-slip dislocations (Hirth and Stair-rod) are generated in the [111] and [11̅0] orientations during compressive deformation, respectively. The L-C structure produced by tensile loading in the [111] orientation and Hirth/Stair-rod dislocations produced in the [11̅0] orientation under compression act as a dislocation pinning and limit the continued glide of the dislocations. The dislocation reactions under various conditions were analyzed, which is helpful to understand the plastic deformation mechanism of CoCrNi alloy.

Designing Mg alloys with high strength and ductility by reducing the strength difference between the basal and non-basal slips

The additions of alloying elements can significantly improve the mechanical properties of magnesium (Mg) alloys, mainly due to the fact that their additions change the critical shear stresses (CRSS) for dislocation slips. In this work, experimental and computational methods were used to explore the mechanisms responsible for the roles of Sm element addition in affecting the mechanical properties of Mg. The results showed that the addition of Sm obviously improves the microstructure and mechanical properties. It promotes the formation of twins and beneficially activated the non-basal <a> slip at the initial stage of plastic deformation, resulting in a high ductility. The Visco-Plastic Self-Consistent (VPSC) and the two-beam diffraction results confirmed that the pyramidal <c + a> slip and prismatic <a> slip were activated during tensile testing. The quantitative analysis of slip traces verified that the volume of non-basal slips reached 35 % after Sm addition. The additions of Sm with solid solution increased the activities of pyramidal <c + a> dislocation during deformation, which was beneficial to accommodate the c-axis strain, and finally improved the room temperature ductility of Mg. First-principle calculations demonstrate that the solute Sm atoms would reduce the stacking fault energy for basal and prismatic slips.

On the micromechanism of superior strength and ductility synergy in a heterostructured Mg-2.77Y alloy

Heterostructured metals and alloys are a new class of materials in which mechanical behaviors between the heterogeneous regions are significantly different, and the mechanical properties of bulk materials are superior to the superposition of individual regions. In this paper, three distinct types of heterostructures were constructed in Mg-2.77Y (wt.%) alloy by applying simple thermomechanical processing. Namely, Type I: the non-recrystallized grains of several tens of microns were embedded in the micron-scaled recrystallized grains that were distributed along shear bands and dispersed near grain boundaries; Type II: the aggregations of micron-scaled recrystallized grains were surrounded by the non-recrystallized grains; Type II: the micron-scaled recrystallized grains dominated the microstructure, and the non-recrystallized regions with diameters of tens of micrometers were surrounded by those fine recrystallized grains. Mechanical tests showed that the material with type III heterostructure had the optimal combination of yield strength and uniform elongation. This is attributed to its remarkable hetero-deformation induced (HDI) strengthening and dislocation strengthening. At the initial stage of plastic deformation (engineering strain below 4%), the rapid accumulation of geometrically necessary dislocations (GNDs) at the interfaces between recrystallized and non-recrystallized regions and between neighboring recrystallized grains lead to the significant HDI strengthening. As deformation proceeded, the HDI strengthening effect gradually decreased, and the traditional dislocation strengthening that was caused by GNDs accumulation at grain boundaries became significant. In-situ electron back-scattered diffraction (EBSD) testing revealed that the non-basal slip in the non-recrystallized regions became more remarkable in the late stage of deformation, which improved ductility and strain hardening of the alloy. These findings provide new insight into the design of high-performance hexagonal close-packed structural materials by using the concept of HDI strengthening.

Unveiling the grain boundary-related effects on the incipient plasticity and dislocation behavior in nanocrystalline CrCoNi medium-entropy alloy

• The incipient plasticity and dislocation behavior in nanocrystalline (NC) CrCoNi alloy were systematically investigated and compared with its coarse-grained (CG) counterpart and NC Ni. • Multiple pop-ins appear in the P-h curves of NC and CG CrCoNi alloys but disappear in the curves of NC Ni. • The incipient plasticity is mediated by dislocation nucleation in NC CrCoNi alloy but by GBs in NC Ni. • Chemically complex GBs in NC CrCoNi alloy facilitate dislocation nucleation but impede dislocation propagation. • Spatial restrictions from GBs in NC CrCoNi alloy induce size-dependent pop-in behaviors. The incipient plasticity and dislocation behavior in a nanocrystalline (NC) CrCoNi medium-entropy alloy were systematically investigated in terms of pop-in events during instrumental nano-indentation tests. Quantitative statistical analysis and molecular dynamic simulations were performed to reveal the effects of grain boundaries (GBs) on initial stages of plastic deformation . Multiple pop-in events appeared during loading on the NC CrCoNi. The first pop-in that represents the initial yielding was identified to be controlled by dislocation nucleation, which is in sharp contrast to the continuous elastic-plastic transition mediated by GB mechanisms in NC pure metals. This can be attributed to the sluggish kinetics of the chemically complex GBs (CCGBs) in the NC CrCoNi that hinders diffusive GB activities but facilitates dislocation nucleation. Subsequent pop-ins were also found to be closely related to the extra dragging effects imposed by the CCGBs on dislocation propagation in the NC alloy . Moreover, the extremely small grain sizes and the consequent high-volume fraction of GBs in the NC alloy severely restrict the lengths of dislocation source and the radii of dislocation loop, giving rise to a higher critical stress, smaller activation volume and lower pop-in width as compared with its coarse-grained counterpart. These results provide new insights into the onset of nano-plasticity in concentrated multi-principal element alloys.

Microstructure evolution and shear band formation in an ultrafine-grained Ti–6Al–4V alloy during cold compression

It is generally accepted that dynamic recrystallization (DRX) is the result of shear banding in metallic materials. However, we observed the microstructure evolution in an ultrafine-grained Ti–6Al–4V alloy under quasi-static compression and found the formation of DRX induced micro shear bands at the initial stage of plastic deformation. It is of interest that the strain-localized regions experienced a two-step recrystallization process, thus resulting in the formation of refined dynamic recrystallized (DRX) grains in transition zones and nanograins in core regions of micro shear bands successively. It is suggested that the DRX taking place at local regions led to the strain softening, which subsequently accelerated the formation of micro shear bands. Micro shear bands nucleated, grew wider, multiplied and propagated by means of gradually consuming the DRX regions with the increase of local strains. Those micro shear bands are considered to contribute to synergetic plastic deformation in addition to dislocation slipping at lower strains, while some macro shear bands are regarded as the precursor of fracture at higher strains. Based on the observation results a new DRX mechanism of shear band was proposed. The experimental results in the present work can provide new evidences and novel insights of the shear-band formation, plastic deformation as well as failure mode in UFG alloys under quasi-static loading conditions.

Chemical-element-distribution-mediated deformation partitioning and its control mechanical behavior in high-entropy alloys

• Effect of chemical heterogeneities on plasticity and strength is studied using atomic simulations in high-entropy alloys. • Elemental anisotropy/difference factor is proposed, and then used to evaluate the short range order and predict the HEA properties. • Elemental anisotropy factor for optimal high performance is accurately estimated by machine learning. • By a machine learning approach coupled with MD simulations, elemental anisotropy ranges from 2.9 to 3. The chemical element distributions always strongly affect the deformation mechanisms and mechanical properties of alloying materials. However, the detailed atomic origin still remains unknown in high-entropy alloys (HEAs) with a stable random solid solution. Here, considering the effect of elemental fluctuation distribution, the deformation behavior and mechanical response of the widely-studied equimolar random CoCrFeMnNi HEA are investigated by atomic simulations combined with machine learning and micro-pillar compression experiments. The elemental anisotropy factor is proposed, and then used to evaluate the chemical element distribution. The experimental and simulation results show that the local variations of chemical compositions exist and play a critical role in the deformation partitioning and mechanical properties. The high strength and good plasticity of HEAs are obtained via tuning the chemical element distributions, and the optimal elemental anisotropy factor ranges from 2.9 to 3 using machine learning. This trend can be attributed to the cooperative mechanisms depending on the local variational composition: massive partial dislocation multiplication at an initial stage of plastic deformation, and the inhibition of localized shear banding via the nucleation of deformation twinning at a later stage. Using the new insights gained here, it would be possible to create new metallic alloys with superior properties through thermal-mechanical treatment to tailoring the chemical element distribution.

Achieving the strength-ductility balance of boron nitride nanosheets/Al composite by designing the synergistic transition interface and intragranular reinforcement distribution

The distribution state of reinforcement in matrix plays a significant role in affecting the strength-ductility relationship in metal matrix composites. Restricted by the great distinction in geometrical size, intrinsic properties and the poor wettability, the discontinuous reinforcement particulates are commonly accustomed to being distributed at grain boundaries and thus being stuck in the disadvanced stress concentration near the interface. Herein, we report a strategy to realize the special in-situ intragranular AlN nanoparticles together with a well-bonded intergranular two-dimensional transition nanosheets/metal interface structure in boron nitride nanosheets (BNNSs)/Al system through the integrated segmented ball milling (SBM) and reaction sintering route. It is revealed that the BNNSs-AlN-Al transition interface can effectively alleviate the stress partitioning at the interface in the initial stage of plastic deformation. And the coherent intragranular AlN/Al interface benefits to a strong interfacial bonding and leading to the multiplication of intragranular dislocations during the subsequent deformation. The combined effect improved the deformation uniformity of the composites and delayed the crack propagation. As a result, a high strength-ductility balance was achieved in BNNSs/Al composites. The present work may provide a new protocol for achieving high strength-ductility synergy for metal matrix composites.

Effect of Plastic Deformation and Subsequent Heat Treatment on the Acoustic and Magnetic Properties of 12Kh18N10T Steel

This paper presents results from studies on the effect of plastic deformation and subsequent heat treatment on the acoustic and electromagnetic properties of 12Kh18N10T austenitic steel. Widely used in industry, 12Kh18N10T cryogenic corrosion-resistant austenitic steel is interesting because upon plastic deformation the martensitic phase within it occurs, which significantly changes the electromagnetic, elastic, and strength properties of the material. The formation of a new phase together with the process of plastic deformation affects the crystallographic texture of the alloy, which impacts such parameter as acoustic anisotropy. Changes in the magnetic properties connected with appearance of the ferromagnetic phase of martensite in the paramagnetic austenite matrix were detected with an eddy current ferrite meter. It is found that, at the initial stage of plastic deformation (uniaxial tension), the value of the acoustic anisotropy parameter decreases. Probably, this is connected with the fact that the change in the texture is more affected by the deformation of austenite than the formation of α′-martensite. Further deformation of the material causes more intense formation of the new phase and its impact on the crystallographic texture becomes predominant, which results in the increase in the parameter of acoustic anisotropy. It is also found that annealing of 12Kh18N10T pre-deformed stainless steel at temperatures of 350, 600, 700, and 1050°C decreases the parameter of acoustic anisotropy and the volume content of the magnetic phase. At the temperature of 600°C, the acoustic anisotropy of the material drops to zero, whereas at the temperature of 1050°C, the martensitic phase is completely disintegrated and the texture is determined only by the austenitic phase.

The role of {111} slip in the initial plastic deformation of Ni-base superalloys at room temperature

After just yielding at room temperature, the deformation mechanisms in the Ni-base superalloys René N5, CMSX-4, PWA 1483, and CM247LC are investigated by transmission electron microscope. It is found that anti-phase boundary shearing controls the initial plastic deformation of René N5, CMSX-4 and PWA 1483, although stacking fault shearing also operates in the latter two alloys. Whereas, besides many pairs of a/2 〈110〉 dislocations, a high density of isolated superlattice stacking faults and extended stacking faults is also created in CM247LC after around 0.2% plastic deformation, indicating that stacking fault shearing prevails in the initial stage of plastic deformation. These observations demonstrate that plastic deformation is not accomplished solely by anti-phase boundary shearing in Ni-base single crystal superalloys at room temperature, and the formation of superlattice stacking faults does not necessarily require reordering of atoms, hence providing new insights into understanding the interaction mechanisms between matrix dislocations and γ' precipitates.