Crystal Orientation Relationship Research Articles

Effect of Initial Position and Crystallographic Orientation on Grain Selection Procedure in Z-Form Selector for Ni-Based Single-Crystal Superalloy.

The grain selection process in a Z-form selector for Ni-based single-crystal superalloy was simulated using a macro-scale ProCAST software (2013 version) coupled CAFE module combined with an experiment to investigate the grain selection procedure and mechanism with different grain positions and crystal orientation relationships. A non-stationary solidification process was found in the Z-form selector, and the liquid-solid (L-S) interface was tilted in the same direction as the selector channel during directional solidification. Given that the grain boundary was parallel to the Z-form selector, the overgrowth rate of the bi-crystal in the selector channel was very low. The initial position of the bi-crystal in the selector channel has a greater effect on the overgrowth rate than the effects of primary and secondary orientations. The grain selection was a result of the coupling of the competitive grain growth effect and geometrical restriction effect. Finally, the selection grain mechanism within the Z-form selector was discussed, coalescing the temperature field and the grain competition growth mechanism.

Terahertz sum-frequency excitation of coherent optical phonons in the two-dimensional semiconductor WSe2

Driving fundamental excitations via strong light fields is one of the most important issues in solid state physics, which opens up new avenues to control material properties. Two-dimensional materials are fruitful platforms for future semiconductor applications, including opto-electronic and phononic devices, yet the phonon dynamics and nonlinear phonon–phonon coupling remain under-explored. Here, we demonstrate coherent phonon excitation in thin films of the layered two-dimensional semiconductor WSe2 induced by intense and broadband ultrafast terahertz (THz) pulses. We performed THz Kerr effect spectroscopy and observed coherent phonon oscillations assigned to the E2g optical phonon mode. The phonon amplitude displays a quadratic THz field strength dependence, indicating a sum-frequency THz excitation process. Furthermore, pump–probe polarization and crystal orientation relationships, supported by symmetry analysis of the nonlinear susceptibility and Raman tensors, provide helpful insight into nonlinear phonon–phonon interactions and potential coherent control schemes for the manipulation of phonon polarization and material properties in WSe2.

Effect of T6 heat treatment on microstructure and mechanical properties of Al–18Si–10Cu–10Ni–5Mn–5Mg alloy prepared by laser-directed energy deposition

The new aluminum alloy Al–18Si–10Cu–10Ni–5Mn–5Mg (wt.%) prepared by laser-directed energy deposition (L-DED) process has excellent mechanical strength but poor ductility. In this paper, a T6 heat treatment is applied to it, aiming at the improvement of the material's ductility. The results show that after the T6 heat treatment, the original fine microstructure of the material is destroyed, and the phase composition changes. However, it is found that the formation of the nano-strengthened θʹ phase and the clear crystal orientation relationship between the θʹ phase and the α-Al matrix make the θ′ phase form a continuous grain boundary in the Al matrix, thus enhancing the strength and hardness of the alloy. It is worth noting that the microhardness is reduced slightly, but the residual stress is almost completely eliminated. The experimental results of mechanical properties show that the tensile strength and compressive strength of the material are reduced by 12 % and 17 % respectively after T6 heat treatment, but the ductility of the material is increased by 1.3 times, which is mainly attributed to the change of strengthening mechanism and the large and uniform second phase.

The phase decomposition in non-equimolar (ZrHfVNbMoW)Cx complex concentrated carbides via carbon content regulation

(Zr0.196Hf0.02V0.196Nb0.196Mo0.196W0.196)Cx complex concentrated ceramics (CCC) with variable carbon non-stoichiometry are fabricated by hot-pressing sintering at 2100 °C for 1 h. The influence of carbon content on phase decomposition behavior and microstructural evolution is investigated. With the decreasing carbon content, the phase transformation of single-phase solid solution → discontinuous precipitation → spinodal decomposition → single-phase occurs, consistent to the binary phase diagram with miscibility gap. The single-phase solid solution decomposes into (ZrHfNb)C-rich and (VMoW)C-rich phases during the phase separation. For spinodal decomposition, the nodular microstructure is formed with coherent crystal orientation relationship of (ZrHfNb)C-rich phase {011} // (VMoW)C-rich phase {011}. The spinodal decomposition leads to in-situ hardening and toughening effects due to the interface hardening and fine microstructure. The spinodal decomposition into two high entropy phases could potentially be beneficial to tailor properties and demonstrated in a future work.

Contribution made by double-sized TiC particles addition to the ductility–strength synergy in wire and arc additively manufactured Al–Cu alloys

An Al–Cu matrix composite reinforced with uniformly-distributed micron- and nano-double-sized TiC particles (MNDS-TiCps) was successfully fabricated using a wire and arc additive manufacturing (WAAM) process. The combined effect of the MNDS-TiCps on the precipitation of the θ″ phase, the structural evolution of the grain boundaries, and solidification dynamics of the deposited Al–Cu matrix composites were subsequently investigated. The micron-sized TiC particles in the molten pool generate nucleation undercooling (ΔTnu, ∼0.32 K) which inhibits grain boundary segregation due to constitutional undercooling and promotes the redistribution of the Cu solute in the Al matrix. The phase composition at the grain boundaries changes from θ-Al2Cu to α-Al + θ-Al2Cu and the non-coherent interface between the α+θ transition zone and θ grain boundary is transformed into a coherent interface between the α+θ grain boundary and Al matrix, i.e. (211)θ-Al2Cu//(111)Al. The decrease in free energy within the Al matrix provides energy to facilitate the growth of nuclei on the surface of the nano-sized particles. A semi-coherent interface is thus detected between the TiC and precipitates, characterized by a crystal orientation relationship of (200)TiC//(310)θ″-Al2Cu. The dislocations that provide pipe-diffusion paths for solute Cu constitute a driving force that coarsens the precipitates, promoting the precipitation of θ″ precipitates. Multi-site co-deformation combined with dislocation increment inhibits stress damage to the micro-interface. The strength and elongation increase by 51.0 % and 118 %, respectively, compared to specimens without TiC. This work provides a novel perspective for tailoring WAAM-deposited Al–Cu alloys by achieving favorable structural evolution in the grain boundaries, inducing the precipitation of precipitates, and yielding outstanding synergy between ductility and strength.

Improvement of Magnetic Properties of Zn-bonded Sm-Fe-N Magnets and Investigation of Microstructural Changes at Sm<sub>2</sub>Fe<sub>17</sub>–Zn Interface

This paper reviewed development of Zn-bonded Sm-Fe-N magnets in our group, and reported interfacial diffusion and phase changes at the Sm2Fe17–Zn interface during annealing. For increasing magnetic properties of Zn-bonded Sm-Fe-N magnets, decreasing oxygen content, improving dispersibility of Zn, and increasing relative density are necessary, therefore we prepared low oxygen content Sm-Fe-N and fine Zn powders. The powders were sintered by spark plasma sintering process for increasing density under low oxygen atmosphere resulting in obtaining high (BH)max of 200 kJm-3 with relatively high coercivity of 1.28 MAm-1 and β(HcJ) of –0.34%C-1. In order to further improve the (BH)max, it is necessary to control interfacial diffusion and reaction between Sm2Fe17N3 and Zn phases. Thus, as a first step, microstructural changes and interdiffusion coefficient at the Sm2Fe17–Zn interface were investigated using Sm2Fe17–Zn diffusion couples, in this study. It was clear that interdiffusion of Zn, Fe and Sm occurred during annealing below melting temperature of Zn, and the diffusion rate of Zn was faster than those of Fe and Sm. Furthermore, with Zn diffusing into Sm2Fe17 phase, the Sm2Fe17 decompose to ThMn12-Sm(Zn,Fe)12 and α-FeZn phases with specific crystal orientation relationship.

Creep Deformation Behavior and Microstructure of Laves-strengthened Ferritic Heat-resistant Steels Containing Nitrogen or Carbon

The creep deformation behavior and microstructure of a N-containing steel expected to exhibit high creep strength and excellent oxidation resistance were investigated. Even for steel with a high W content, it was possible to form a martensitic microstructure by adding a sufficient amount of N. Comparison of the microstructures of the N-containing steel and a C-containing steel confirmed that the two steels have the same crystal orientation relationship. The N-containing steel precipitated with the Laves phase as a strengthening phase displayed a higher creep strength than conventional steel under relatively high stress. However, the superiority of the creep strength of the N-containing steel relative to the conventional steel decreased under low stress. The stress exponent of the N-containing steel was different from those of the C-containing steel and the conventional steel. This deference considered to be ascribed to the difference of variation behavior of dislocation density during creep deformation.

Achieving strength-ductility synergy in semi-solid squeeze cast 6TiB2/Al–17Si–4Cu composites by heat treatment

This study aims to achieve synergistic strength-ductility enhancement of semi-solid squeeze cast 6TiB2/Al–17Si–4Cu composites through in-situ particle strengthening and T6 heat treatment. The microstructure and mechanical properties of 6TiB2/Al–17Si–4Cu composites with different heat treatments were investigated. TiB2 particles are semi-coherent with α-Al and primary Si, respectively. The nanoscale precipitate phases were determined by their crystal orientation relationships. The results showed that they are θ and θʹ phases. Meanwhile, the research results pertaining to the mechanical properties imply that the strength and ductility are enhanced by the TiB2 particles and Al2Cu precipitates. The optimum heat treatment process (solution treatment for 9 h at 520 °C and aging for 8 h at 170 °C) of strengthened 6TiB2/Al–17Si–4Cu composites is revealed in this study, when the ultimate tensile strength and elongation of the composites are 263.3 MPa and 0.51%, respectively. The mechanisms governing the enhanced strength and ductility of 6TiB2/Al–17Si–4Cu composites were discussed.

Microstructure of Glidcop AL-60

Glidcop is an oxide-particle-dispersion strengthened copper composite that has a combination of high mechanical strength and high electrical conductivity. It has been used as a conductor for the 100 T ultrahigh field pulsed magnet by the National High Magnetic Field Laboratory, USA. In the quest for even higher field pulsed magnets, material development is crucial. Since the mechanical properties of a material are often determined by its microstructure, full characterization of the microstructure of Glidcop is necessary. In this work, we studied the microstructure of Glidcop AL-60 using both transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). We identified both α-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and cubic η-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles in AL-60 and investigated their size and density distribution. The η-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles with typical size of 5 to 30 nm are of triangular shape. They have well defined crystal orientation relationship with the Cu matrix. We observed dislocations pinned by the alumina nanoparticles in cold-drawn wires. We believed that dislocation bypassing alumina particles via Orowan looping was the main strengthening mechanism. We observed microcracks near large particles, demonstrating the detrimental effect of large particles in AL-60.

Impact of crystal orientation relationship on microstructure evolution in Al-Ag-Cu ternary eutectic

The invariant ternary eutectic of the Al–Ag–Cu system can solidify with a variety of microstructural patterns for which differences in processing conditions are only partially responsible. Particularly, the occurrence of non-chain-like patterns has not yet been fully analyzed and described, especially regarding the role of crystallographic orientations. To evaluate the impact of the crystallographic orientations on the microstructural pattern formation within directionally solidified Al–Ag2Al–Al2Cu, a survey of previous work on orientation relationships in this and other three-phase eutectics was conducted, then a systematic experimental study carried out on multiple eutectic grains within a single sample at different solidification distances using scanning electron microscopy and electron backscatter diffraction. Eutectic grains with chain-like and non-chain-like patterns were analyzed and the orientation relationships between the three phases were determined. Building off earlier work, the relation between highly ordered chain-like patterns and their orientation relationships is further elucidated and an overall correlation of less-ordered non-chain-like patterns with their orientation relationship is established. Thus, a mechanism for non-chain-like pattern evolution at nucleation and during growth regarding the present orientations is proposed, which can serve as a basis for controlled microstructure adjustments.

Coarsening mechanism of T1 precipitation and calculation of T1/Al interface properties in 2198 Al–Cu–Li alloys: Experimental and DFT studies

This paper aims to reveal the thickening mechanism of multiple different types of T1 precipitation through experimental characterization by HAADF-STEM. Meanwhile, a detailed theoretical analysis of the properties of the T1(0001)/Al(111) interface has been carried out for the first time by applying the first-principles. The experimental results show that the crystal orientation relationships of the T1/Al interface are (0001)T1/{111}Al and [1010]T1/[110]Al. Firstly, two T1 phase thickening mechanisms are proposed. (i) The Cu-rich layer in the T1 phase is used as a substrate for the coarsening of the precipitation. (ii) The Al–Cu transition layer is used as a starting point for precipitation thickening. Secondly, the first-principles were applied to calculate the properties of the T1/Al interface in terms of adhesion work, interfacial energy and electronic structure. The results of the interfacial energy and adhesion work calculations demonstrate that the AlLi-terminated T1/Al interface is more stable. The analysis of the electronic characteristics of the interface shows that the AlLi-terminated interface is more stable and that strong Al–Al and weak Al–Li covalent bonds are formed at the T1/Al interface. Meantime, the electronic structure features are in complete agreement with the findings of the energy calculations.

ReciPro: free and open-source multipurpose crystallographic software integrating a crystal model database and viewer, diffraction and microscopy simulators, and diffraction data analysis tools

ReciPro is a comprehensive multipurpose crystallographic program equipped with an intuitive graphical user interface (GUI), and it is completely free and open source. This software has a built-in crystal database consisting of over 20 000 crystal models, and the visualization system can seamlessly display a specified crystal model as an attractive three-dimensional graphic. The comprehensive features are not confined to these crystal model databases and viewers. It can smoothly and quantitatively simulate not only single-crystal and/or polycrystalline (powder) diffraction patterns of X-ray, electron and neutron diffraction of a selected crystal model, based on the kinematic scattering theory, but also various electron diffraction patterns and high-resolution transmission electron microscopy (TEM) images, based on the dynamical scattering theory. The features of stereographic projection of crystal planes/axes to explore crystal orientation relationships and the semi-automatic diffraction spot indexing function for experimental diffraction patterns assist diffraction experiments and analyses. These features are linked through a user-friendly GUI, and the results can be synchronously displayed almost in real time. ReciPro will assist a wide range of crystallographers (including beginners) using X-ray, electron and neutron diffraction crystallography and TEM.

Effect of Cu Content on the Precipitation Behaviors, Mechanical and Corrosion Properties of As-Cast Ti-Cu Alloys.

Ti-Cu alloys have broad application prospects in the biomedical field due to their excellent properties. The properties of Ti-Cu alloys are strongly dependent on Cu content, microstructures, its Ti2Cu phase and its preparation process. The aim of this work is to investigate the effect of Cu content on the precipitation behaviors, mechanical and corrosion properties of the as-cast Ti-Cu alloys. The microstructures and phase evolution were characterized by SEM and TEM, and the properties were studied by tensile and electrochemical test. The results show that the volume fraction of Ti2Cu phase increases with the increase of Cu content. The Ti2Cu phase presents a variety of microscopic morphologies with different Cu content, such as rod, granular, lath and block shaped. The crystal orientation relationships between the Ti2Cu and α-Ti matrix in Ti-4Cu and Ti-10Cu alloys are (103)Ti2Cu//(0[111)α-Ti, [01]Ti2Cu//[20]α-Ti, and (103)Ti2Cu//(0002)α-Ti, [31]Ti2Cu//[110]α-Ti, respectively. The tensile strength, Vickers hardness and Young’s modulus of the Ti-Cu alloys increase with the increase of Cu content, whereas the elongation decreases. The fracture morphologies of these alloys reveal ductile, ductile-brittle hybrid, and cleavage brittle mode, respectively. The corrosion resistance of the Ti-Cu alloys in SBF solution can be described as: Ti-4Cu alloy > Ti-10Cu alloy > Ti-7Cu alloy. The volume fraction of Ti2Cu phases and the “protective barrier” provided by the fine lath Ti2Cu phases strongly affected the electrochemical performances of the alloys.

Crystal orientation relationships and pattern evolution in directionally solidified Al-Cu-Mg ternary eutectic

Understanding the mechanisms of microstructure evolution during alloy solidification is crucial in designing multi-phase, multi-component systems. In the current work, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques are deployed to carry out a detailed experimental investigation to better understand the correlation between crystallographic orientation relationships (ORs) and the microstructural pattern evolution of directionally solidified Al-Al2Cu-Al2CuMg ternary invariant eutectic. The behavior of the patterns in response to imposed low (6 K/mm) and high (25 K/mm) thermal gradients is also presented. Close examination of the microstructure revealed an unexpected modification of lamellar growth, with lamellar sheets being limited in length to approximately four times the width of one sheet, and the Al2Cu rod phase aligning along these pre-existing boundaries which correspond to low index crystallographic planes. Alignment of the pattern was found to increase with increasing thermal gradient. The results shed more light on somewhat contradictory literature data and provide an increased understanding of pattern evolution in multi-phase eutectic systems.

Effect of Ti-doping on peeling resistance of primary M7C3 carbides in hypereutectic Fe[sbnd]Cr[sbnd]C hardfacing coating and γ-Fe/M7C3 interfacial bonding strength

Alloying element Ti plays an important role in improving the mechanical properties of hypereutectic FeCrC hardfacing coating, but its peeling resistance have been neglected. Here, the hardness and wear rate of the hypereutectic FeCrC and FeCrCTi hardfacing coatings were measured. The crystal structure and orientation relationship of primary M7C3 carbide and eutectic austenite matrix were confirmed. Then, the interface properties of γ-Fe//M7C3(Ti) interface were calculated by first principles. The results show that the micro-Vickers and macroscopic Rockwell hardness of the FeCrCTi hardfacing coating are increased, and its wear rate is decreased from (4.33 ± 0.333) × 10−6 mm3/Nm to (3.64 ± 0.366) × 10−6 mm3/Nm. The Ti-doping can effectively inhibit the initiation and propagation of cracks and improve the peeling resistance of M7C3 carbide. Meanwhile, the orientation relationship of eutectic austenite/primary M7C3 carbide is γ-Fe(111)//(Cr, Fe)7C3(101¯0). Among CFe1, CrFe1 and FeFe1 interfaces, interface energy of FeFe1 model is the smallest (1.954 J/m2), and its adhesion work (Wad) is the largest (0.756 J/m2). Moreover, Wad of Ti-doped interface (4.123 J/m2) is larger than that of FeFe1 one (3.045 J/m2) after relaxed, which indicates Ti-doping is beneficial to enhance adhesive strength between γ-Fe//M7C3 interfaces, which improves the peeling resistance of M7C3 carbide.

Locked-lamellar eutectic growth in thin Al-Al2Cu samples: In situ directional solidification and crystal orientation analysis

We investigated the directional-solidification dynamics of slightly hypoeutectic Al-Al2Cu alloys in thin samples. Our goal was to establish a link between the growth of locked, tilted-lamellar patterns and the crystal orientation relationship (OR) between the Al-rich solid solution α and the Al2Cu intermetallic θ, as well as to gain information on the OR-dependent anisotropy of the surface energy γ of the α-θ interphase boundaries. Thin Al-Al2Cu films of thickness of 13±2μm were prepared by plasma sputtering. During solidification at pulling velocities between 0.05 and 0.5μms-1, the coupled-growth front was observed in situ with a long-distance optics. The growth of millimeter-sized eutectic grains was thus followed in real time during transient and steady-state regimes. The orientation of α and θ crystals was measured ex situ by X-ray diffraction and electron backscattering diffraction. In several eutectic grains, a {123}α plane and a {100}θ plane were found to be closely parallel to each other. These coincident planes define a new family of (type-C) ORs in the Al-Al2Cu eutectic, which are distinct from the prevailing ORs that have been previously identified in bulk samples. Crucially, the inclination of the lamellae was systematically close to that of a {100}θ lattice plane, which therefore corresponds to a deep γ minimum in eutectic grains with a type-C OR, or a neighbor one. We initiated a discussion on the selection of the OR, the formation of “stray” eutectic grains, and the lamellar-growth dynamics at eutectic-grain boundaries.

Effects of Co Addition on the Microstructure and Properties of Elastic Cu-Ni-Si-Based Alloys for Electrical Connectors.

The properties and microstructure evolution of quaternary Cu-Ni-Co-Si alloys with different Ni/Co mass ratios were investigated. The microstructure and morphological characteristics of the precipitates were analyzed by using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties and conductivity of the alloys were significantly improved after the addition of Co. The grains presented an obvious growth trend with an increase in Ni/Co mass ratios, and the appropriate Co accelerated the recrystallization process. The δ-(Ni, Co)2Si phases of the Cu-Ni-Co-Si alloys and δ-Ni2Si phases of the Cu-Ni-Si alloys shared the same crystal structure and orientation relationships with the matrix, which had two variant forms: δ1 and δ2 phases. The precipitates preferential grew along with the direction of the lowest energy and eventually exhibited two different morphologies. Compared with that of the Cu-Ni-Si alloy, the volume fraction of precipitates in the alloys with Co was significantly improved, accompanied by an increase in the precipitated phase size. The addition of Co promoted the precipitation of the precipitated phase and further purified the matrix. A theoretical calculation was conducted for different strengthening mechanisms, and precipitation strengthening was the key reinforcement mechanism. Moreover, the kinetic equations of both alloys were obtained and coincided well with the experimental results.

Investigate on the phase interfaces and performance evaluation of TiB2p/Al–Si–Cu–Zn (T6) composites

In this paper, the microstructures, mechanical properties, and corrosion behavior of xTiB2/Al–9Si–3Cu-0.8Zn composites after T6 heat treatment were invested in detail through the combination of different technologies, including optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile testing, corrosion testing, etc. The research results showed that the average size of the α-Al grains gradually decreased with the increase of TiB2 particles (TiB2p) content. In addition, there was a semi-coherent relationship between TiB2p and the α-Al matrix, and the nanoscale precipitates were identified as θ and θʹ phases by virtue of their crystal orientation relationship. Tensile testing results revealed that an increase in TiB2 content caused the elastic modulus, yield strength and tensile strength of the composites to increase and then decrease. And with a TiB2p content of 4 wt%, they reached 85.7 GPa, 360 MPa and 398 MPa, reflecting increases of 26.2%, 60.0%, and 30.9%, respectively. The contributions of thermal mismatch, grain boundary and Orowan strengthening mechanisms to the overall yield strength of the 4%TiB2/Al–9Si–3Cu–0.8Zn composite were 72.1, 3.8, and 35.6 MPa, respectively. Unfortunately, the corrosion resistance of xTiB2/Al–9Si–3Cu–0.8Zn composites gradually decreased with increasing TiB2p content. The corrosion morphology analysis indicated that the agglomeration of TiB2p and Si weakened the protection afforded by the oxide film, evolving into a point of nucleation for the subsequent corrosion reaction. Moreover, point–pair correlation was observed between the TiB2p and Al matrix, exacerbating the corrosion. The results implied that extra factors be considered in industrial application of TiB2 ceramic particles in a metallic system.

Simultaneously enhanced hardness and electrical conductivity in a Cu–Ni–Si alloy by addition of Cobalt

The effects of Co on the physical properties and precipitation evolution of a Cu–Ni–Si alloy are investigated via hardness and electrical conductivity testing, transmission electron microscopy and a quantitative three-dimensional atom probe. The precipitation sequence of Cu–Ni–Si alloy aging at 500 °C can be expressed as supersaturated solid solution → solute clusters → GP zones → Ni2Si phases. In the early aging stage, the formation of atomic clusters is accompanied by the occurrence of spinodal decomposition. The addition of Co accelerates the redistribution and agglomeration of solute atoms, resulting in the nucleation of (Ni, Co)2Si phases directly from the supersaturated state, which further hinders atomic cluster formation and spinodal decomposition. The Ni2Si and (Ni, Co)2Si phases, which are divided into a region II containing pure Ni2Si and the (Ni, Co)2Si phase and an unstable region I containing a small amount of Cu atoms, show the same crystal structure and orientation relationship with the matrix. During the aging process, the range of region I is gradually replaced by the core stable region II and accompanied by the growth of the total thickness of the precipitated phase. This remarkable age effect with Co addition can be attributed to the enhanced number of (Ni, Co)2Si precipitates, which simultaneously increases the strength and electrical conductivity.

Crystal Orientation Relationships among Acicular Ferrite, Oxide and the Austenite Matrix in a Steel Weld Metal

Acicular ferrite (AFα) formed on oxide particles in steel weld metals has a positive effect on toughness at low temperature. Good lattice coherency between AFα and oxide is one of the proposed reasons for promotion of AFα formation. Lattice coherency is affected by crystal structure of oxide and crystal orientation relationship (OR) between oxide and AFα. In the present study, ORs among AFα, oxide and γFe are investigated in a low carbon steel weld metal. Cube-cube (C-C) OR is observed between γFe and the oxide. It is probable that the oxide liquefied at high temperature, and then crystalized having the C-C OR with the surrounding γFe during cooling in welding process. Near Kurdjumov-Sachs (K-S) and near Baker-Nutting (B-N) ORs are observed between γFe/AFα and oxide/AFα, respectively. The misorientation from the B-N OR is larger than that from the K-S OR just after nucleation of AFα. This implies that AFα forms satisfying a near K-S OR with γFe essentially. It is supposed that formation of both the C-C (γFe/oxide) and near K-S (AFα/γ) ORs results in apparent formation of the near B-N OR between oxide and AFα.