Crystallographic Orientation Relationship Research Articles

Investigation of microstructure evolution and mechanical properties of near-eutectic Fe2-yCoNiCryCx high entropy cast iron

Near-eutectic Fe2-yCoNiCryCx high entropy (HE) cast iron was designed and characterized. The FeCoNiCrC0.45 eutectic HE cast iron was determined being composed of FCC phase and M7C3 carbide. Their crystallographic orientation relationship at the outer region is [101]//[01 1‾ 0] and {110}//{112‾ 0}. The orientation of eutectic M7C3 carbide changes from [01 1‾ 0] to [123‾ 0] as the grain grows from the outer to inner of sample. With the increase of carbon addition, the alloy composition transits from hypoeutectic to hypereutectic where the primary phase changes from FCC phase to M7C3 carbide. With the increase of chromium addition, the phase constituent transits from a mixture of FCC, M7C3 and graphite to that only with FCC and M7C3. The yield strength, compressive strength and hardness for Fe2-yCoNiCryCx HE cast iron are more sensitive to the chromium than carbon. Fe1.2CoNCr0.8C0.45 HE cast iron exhibits the superior properties with the ultimate strength of 1934 MPa and elongation rate of 21.3%, which is mainly attributed to the strengthening mechanism induced by the precipitation of M7C3 carbide with higher fraction. It provides a clue for the design of new cast iron with high-strength, high-elongation and high-hardness.

Spinodal Decomposition in Natural Bornite–Chalcopyrite Intergrowths: A Way of Cu-(Fe)-Sulfide Mineral Growth

Spinodal decomposition is an important mechanism of exsolution. However, spinodal decomposition has not been observed in natural sulfide intergrowths. We utilized focused ion beam (FIB) and transmission electron microscopy (TEM) techniques to confirm spinodal decomposition in natural sulfide intergrowths (chalcopyrite and bornite). According to FIB and TEM analyses, spinodal decomposition occurred as small and curving alternating dark and bright fluctuations in natural bornite–chalcopyrite intergrowths. Due to the low temperature that drove the exsolution mechanism, fluctuations ~10 nm wide and 20–200 nm long contained non-stoichiometric and tetragonal bornite and chalcopyrite. The corresponding electron diffraction of spinodal decomposition displayed a satellite spot in the [−210] direction for bornite, and the (200)* and (224)* of chalcopyrite paralleled the (24−2)* and (242)* of bornite, respectively. These observations all agreed with spinodal decomposition, two coexisting phases formed with a crystallographic orientation relationship, which indicated the first observation of spinodal decomposition in natural sulfide intergrowths. These findings confirmed that spinodal decomposition is a mechanism for natural crystal growth. As spinodal decomposition is larger in extent and faster than nucleation and growth, other Cu ore deposits may also form via this mechanism.

Crystallographic analysis of Ga+ irradiation-induced phase transformation in austenitic stainless steels

Focused ion beam processing with Ga+ ion sources is widely applied for nanoscale fabrication of materials and preparation of specimens for advanced microstructural observation by methods such as transmission electron microscopy and 3D atom probes. It is important to suppress specimen damage and microstructural changes associated with Ga+ irradiation, but limited information is available on the mechanism of microstructural changes. In this study, we explored the mechanism of Ga+ irradiation-induced phase transformation of an austenitic stainless steel. The irradiation-induced fcc-bcc phase transformation was characterized by microstructural observations of surfaces and cross sections of specimens and analyses of crystallographic orientation relationships. The results of microstructural analysis showed that the formation of the irradiation-induced bcc phase on the specimen surface increased with increasing irradiation dose. At the same irradiation dose, the bcc transformation initiated sooner, and the total amount of transformation was higher, for irradiation of the (111)fcc planes than the (001)fcc planes. Microstructural analysis of cross-sections showed that irradiation (8.0 × 1016 ions/cm2) of the (001)fcc and (111)fcc planes caused formation of a transformation phase to depths of 100 nm and 60 nm, respectively; the bcc transformation extended to deeper regions in the (001)fcc planes than the (111)fcc planes. In addition, these transformation areas extended over a wider area than the areas of high Ga concentration. The crystallographic orientation relationship before and after the transformation was not a specific orientation relationship, such as Kurdjumov–Sachs or Nishiyama-Wasserman, and its distribution differed depending on the direction of Ga+ irradiation. The mechanism of fcc-bcc phase transformation of SUS304 steel by Ga+ ion irradiation was explained by chemical and stress effects due to the injection of Ga+ ions. Furthermore, the transformation behavior, which depended on the irradiation direction, was discussed in terms of the (111)fcc orientation angle relative to the irradiation direction.

Refinement of carbide precipitates in high-Nb TiAl by cyclic aging treatments

High-Nb TiAl alloys are considered as new generation of γ-TiAl alloys for applications at higher service temperatures owing to their superior high-temperature oxidation and creep resistance. Addition of C element can further improve its high temperature creep resistance through solid solution strengthening and precipitation strengthening, but the coarse carbide precipitates are not conducive to the mechanical performance improvement. This paper provides a method for refinement of carbide precipitates via solution and cyclic aging treatments in an as-cast Ti-45Al-8Nb-0.9C (at%) alloy. Coarse primary carbides that precipitated during casting were eliminated through solution treatment, while numerous submicron secondary carbides were precipitated through cyclic aging treatments. The crystallographic orientation relationship between the precipitated submicron secondary carbides and the high-Nb TiAl matrix was determined by various transmission electron microscopy characterization methods. This refinement method provides a possible way for refinement of other precipitates in TiAl alloys.

Precipitation of Ti2Al phases at lamellar interfaces in a high-Nb-containing TiAl alloy during thermal exposure

The thermal stability of microstructures is crucial for determining the performance of alloys in extreme environments. In the present work, the microstructural evolution and precipitation behavior in a high Nb-containing Ti45Al8Nb alloy during thermal exposure at 950 °C were investigated. It was found that excess α2 phases in the as-cast microstructure were unstable and tended to decompose during thermal exposure. Hexagonal Ti2Al phases precipitated at lamellar interfaces and had a [11¯0]γ∥[112¯0]α2∥[112¯0]Ti2Al, (002)γ∥(11¯00)α2∥(11¯00)Ti2Al crystallographic orientation relationship (OR) with the matrix. Stacking faults (SFs) generated in α2 phases during the α2 → γ phase transformation provided favorable nucleation sites for Ti2Al phases.

Mincy mesosiderite metallic nodules analyzed byEBSD: An approach to understanding their thermal history

AbstractMeteorites carry information about the most common processes that have been active in the early solar system. In particular, mesosiderites are meteorites with a structure considered to be composed of equal parts of iron–nickel metal and silicates. A natural delimitation in the study of such complex systems is the discrimination of the iron–nickel metallic and silicate domains. In this work, we focus on the metallic phases of the Mincy mesosiderite, a specimen available at the Instituto de Ciencias Astronómicas, de la Tierray y del Espacio repository. In Mincy, the metallic phases are iron–nickel–carbon alloys that are distributed forming metallic lumps or pebbles (referred to as metallic nodules in the article) in which kamacite and taenite are present, and taenite is found both at the kamacite/silicate interface and surrounded by kamacite, that is, isolated from the silicates. We made use of the electron backscattered diffraction technique to determine the crystallographic orientation relationships along the taenite/kamacite boundaries as well as for characterizing the (hkl)‐specific grain boundaries regarding the underlying tilt, twist, or twinning mechanism to assist the interpretation of the phase transformations and mechanisms that could explain the formation of these metallic nodules. From the results, each of the metallic nodules has a unique temperature–pressure history and kinetics to undergo phase transformations (mainly partial melting, heterogeneous nucleation‐controlled solidification, and possible evaporation–condensation) as well as liquid‐phase sintering and recrystallization in its own way.

Microstructure and Properties of TiAl Composite Coatings Prepared by Laser Cladding under Multi-Phase β0/CoAl2Ti Phase Strengthening

Ceramic-reinforced TiAl matrix composite coatings are fabricated by laser cladding on Ti-6Al-4V (TC4) surfaces. The present work focuses on matching of the ceramic phase with the TiAl matrix to achieve a strength–toughness matching through the multi-scale multi-phase structure. The results indicated that the structure of composites coatings, including γ, α2, β0, CoAl2Ti, and TiC phases, significantly improved the properties of the composite coatings. The TiAl composite coating reached a maximum hardness of 741.17 Hv0.2, and the 10 at% tungsten carbide (10 WC) coating has the lowest wear volume of 8.8 × 107 μm3, the friction performance was approximate five times that of TC4. Detailed explanation of the friction properties and friction mechanism of the composite coating based on crystallographic orientation relationships and nanoindentation results. The study found that strength–toughness matching is important for the improvement of friction performance. Based on the TiAl alloy generated in the non-equilibrium solidification state in this paper, the solidification process and microstructure evolution are analyzed in detail.

The effects of continuous and discontinuous β-Mg17Al12 on compression creep properties of Mg-8.0Al-1.0Nd-1.0Gd alloys

The microstructure evolution of β-Mg17Al12 in as-cast Mg-8.0Al-1.0Nd-1.0Gd alloy during 420 °C solution and then 210 °C aging treatment was investigated. The results indicate that the discontinuous precipitation (DP) distributes along grain boundaries, and the needle-shaped continuous precipitation (CP) with crystallographic orientation relationship (OR) of [1‾101]Mg//[334‾]β, (01‾11)Mg//(313)β, (1‾011‾)Mg//(33‾0)β are the main intragranular precipitated phases. Compression creep tests of the specimens were carried out at a stress of 60 and 90 MPa at 150 and 180 °C. The microstructure observation reveals that the considerable 86° {101‾2} tension twins assist in the creep deformation for all crept specimens. The solid solution treated alloys achieve excellent creep resistance compared with the aged alloys owing to the strong co-segregation between Nd and Gd in α-Mg and β-Mg17Al12 at 180 °C/90 MPa. However, the creep properties of the aged alloys are superior to that of the solid solution treated alloys at 180 °C/60 MPa and 150 °C/90 MPa, which can be attributed to the inhibited dislocation slipping via needle-shaped and spherical CP. In addition, increasing the CP region and reducing recrystallized grains could improve the creep resistance. Combining the micro-morphology of creep structure and creep parameters (n, Q), the dominated creep mechanism for solid solution treated alloys is grain boundary sliding (n = 1.5–1.8, Q = 32–36 kJ/mol), while the dislocation climb combined with grain boundary diffusion (n = 4–6, Q = 60–80 kJ/mol) is regarded as the controlling creep mechanism for the aged Mg-8.0Al-1.0Nd-1.0Gd alloys.

A new orientation relationship observed between MC and ferrite in Ti Mo microalloyed steel produced by ultra-fast cooling

A new crystallographic orientation relationship (OR) between MC (M, Ti, and Mo) and ferrite has been observed in microalloyed steel produced by new-generation thermo-mechanical processing (traditional TMCP involving ultra-fast cooling). The selected area electron diffraction (SAED) patterns present strong evidence for the new OR, that is (111)MC//(110)ferrite and 1¯10MC//1¯10ferrite, which hasn't been reported previously in MC/ferrite system. While the precipitates formed in the specimens with traditional TMCP obey the well-known Baker-Nutting (BN) and Nishiyama-Wassermann (NW) ORs. The coordinate transformation matrices for BN, NW and the new OR have also been calculated, which further confirms the uniqueness of the new OR. The interfacial energy for the carbides and ferrite that obey the new OR is higher compared with that of BN and NW ORs, which can be attributed to the energy accumulated and maintained in austenite deformation and ultra-fast cooling stage, and then leads to un-equilibrium precipitates

Study of microstructure and compressive strength of a novel Ti-0.75Al-9.5V alloys manufactured by laser deposition melting

A novel Ti-0.75Al-9.5 V alloy is designed based on the typical Ti-6Al-4V alloy and prepared by laser melting deposition in this study. The microstructure, texture, and properties of the different scanning and building planes of the LMDed samples under a serpentine reciprocating scanning strategy are characterized and tested. It is found that the more rapid cooling rate on the building planes leads to a partial morphology transformation of the α phase from the original rod-like shape to a needle-like shape. Furthermore, different maximum thermal stress gradients result in the formation of (110)β texture and (001)β texture on different building planes while The (110)β // (0001)α crystallographic orientation relation leads to the formation of the (21¯1¯0)α texture on both two building planes during solid-phase transformation. The texture evolution on two different building planes also affects corresponding surface slip and mechanical properties. The (001)β texture leads to parallel surface slip tracks on its building plane. The strong (110)β and (21¯1¯0)α textures increase the Vickers hardness from 348.6 ± 2.6 to 371.5 ± 2.7 HV and the compressive yield strength from 1188.0 ± 1.6 to 1276.5 ± 7.3 MPa but suppress the plastic strain from 16.7 ± 0.9% to 12.6 ± 1.0%. All the samples have their compressive fractural strength nearing 1730 MPa, which is higher than that of the reported LMDed Ti-6Al-4V alloy (1690 MPa).

New insight into precipitation of Al3Zr and correlative effect on recrystallization behavior in a rapidly-solidified Al-Zn-Mg-Cu-Zr alloy

The influence of temperature of first-step pretreatment on the precipitation and crystal structure of Al3Zr in a spray-formed (SFed) Al-Zn-Mg-Cu alloy was systematically explored. With different first-step pretreatments, the microstructure evolutions during hot extrusion and solution treatment were studied. The results show that pretreatment before hot-working is necessary for rapidly-solidified Al-Zn-Mg-Cu alloy and temperature of first-step pretreatment is crucial for stabilizing microstructures. In detailed, the homogenous nucleation of L12 Al3Zr is limited at low first-step temperature (<250°C), while the transformation from L12 Al3Zr to D023 Al3Zr is simulated and high first-step temperature (≥420°C). The crystallographic orientation relationship between D023 Al3Zr precipitate (P) and Al matrix is recognized as: [001]Al//[011]P, (200)Al//(011¯)P, (020)Al//(200)P, which is different from the previous works. When the first-step temperature is 250–350°C, the dispersed η-Mg(Zn,Al,Cu)2 phases formed during spray forming can act as heterogeneous nucleation sites of Al3Zr precipitation. The recrystallization resistance of SFed Al-Zn-Mg-Cu alloy during solution treatment is markedly enhanced by an optimized pretreatment of 250°[email protected] h + 470°[email protected] h.

Eutectoid decomposition of βNb5Si3 → αNb5Si3 + Nbss in Nbss/Nb5Si3 in-situ composites revealed by electron microscopy

Eutectoid decomposition of βNb5Si3 → αNb5Si3 + Nbss in Nbss/Nb5Si3 in-situ composites has been systematically investigated by electron microscopy. βNb5Si3 would transform into different αNb5Si3 orientation variants around 1075 °C. There is no inherent orientation relationship (OR) between βNb5Si3 and αNb5Si3, which might be regulated by the diffusive nature of the transformation. Numerous Nbss precipitates would form within αNb5Si3 with crystallographic OR of <001>Nb// < 001>α. This transformation is promoted by formation of dislocations and the diffusion of Nb at elevated temperatures, which will propagate from Nbss/βNb5Si3 interfaces to the interior of βNb5Si3 grains.

Probing interface structure and cation segregation in (In, Nb) co-doped TiO2 thin films

Atomic-scale exploiting interfacial structure and cation distribution in doped TiO2 thin films possessing a polymorphic structure is of great importance for understanding their film-growth behavior and the structure-property relationship. Here, by applying advanced electron microscopy imaging, we have revealed the atomic-scale microstructure of TiO2 thin films co-doped with In and Nb (TINO) prepared on (001) LaAlO3 substrates by pulsed laser deposition. We determined that the TINO slabs with a brookite-typed structure (B-TiO2) form in the anatase-typed TINO (A-TiO2) film matrix with the crystallographic orientation relationship of (1¯12)[110]A-TiO2//(010)[001]B-TiO2. Besides the polymorphic phase boundary, interface structures including the {112}〈110〉-typed twin boundaries (TBs) in the A-TiO2 films and the (010) stacking faults (SFs) in the B-TiO2 slabs have been characterized. Cation (In and/or Nb) segregation and structure relaxation occur at the TBs and the SFs, which is energetically favorable corroborated by density functional theory calculations. Additionally, the cation segregation in the SFs leads to the formation of a new structure locally. Our findings provide a better understanding of interface structure, cation segregation, and phase formation in the doped-TiO2 polymorph materials.

Corrosion behavior of CoCrNiMoBC coatings obtained by laser cladding: Synergistic effects of composition and microstructure

In order to improve corrosion resistance of stainless steels, a CoCrNiMoBC coating was prepared by laser cladding. The microstructure, composition, and crystallographic orientation relationships of the coating were discussed. Electrochemical methods were used to evaluate its corrosion behavior. Results showed that the coating had remarkable resistance to chloride ion corrosion under strongly acidic conditions. The critical pitting temperature of the coating was higher than 80 °C in both neutral and acidic chloride ion environments. Immersion tests confirmed that pits did not expand significantly after 10 days immersion in 5 M HCl solution. The excellent corrosion resistance stemmed from a stable passivation film formed due to the synergistic effects of composition and microstructure.

In situ combustion synthesis of spherical Si@Si3N4 granules

AbstractSpherical Si@Si3N4 granules were first prepared by in situ combustion synthesis. The inside of the granules is dense without cracks, and the two phases at the interface are well‐bonded. More significantly, no binder was used between the Si3N4 grains on the surface layer, thereby avoiding phonons scattering of metal oxides. In addition, crystallographic orientation relationships between Si and Si3N4 were identified by coupling transmission electron microscopy with selected area electron diffraction technology, and much more potential matching planes are also predicted according to the edge‐to‐edge model. It was found that the minimization of the interfacial energy will promote the formation of a transition layer at the interface, leading to the well‐bonded between core and shell. On the basis of the observations, the underlying growth mechanism of the Si@Si3N4 was comprehensively analyzed and put forward. Benefiting from the remarkable merits, the as‐synthesized Si@Si3N4 granules showed great potential for alternative fillers in solving heat dissipation problems for electronic devices.

Hematite Exsolutions in Corundum from Cenozoic Basalts in Changle, Shandong Province, China: Crystallographic Orientation Relationships and Interface Characters

Here, we present well-oriented hematite exsolutions in corundum megacrysts from Cenozoic basalt in China. Crystallographic orientation relationships (CORs) and the interface characters between the hematite exsolutions and the corundum host were analyzed by electron backscatter diffraction (EBSD) and high-resolution transmission electron microscope (HRTEM), respectively. The CORs and the regular interface confirm the exsolution and the exsolution was formed under depressurization based on the crystal chemistry theory. There are three groups of exsolutions intersected with ~60°. Two groups of the exsolutions have the same orientation with the host and the other group is twinned to those two groups. Focused ion beam (FIB) for HRTEM foil preparation was carried out. HRTEM photographs show that there are periodic coherency units at (0001) interface. The measured unit lengths are 6.71–6.72 nm, which are in good agreement with every 17-DCrn011¯2projection or 16-DHem011¯2projection. Based on the results, the possibility is that at the interface, the hematite-corundum phases tend to modulate to achieve the maximum coherency in the geological process during exsolution. This research is helpful to understand the interface characters between the exsolution and host.

Trace sulfur-induced embrittlement of ultrahigh-purity copper

Sulfur (S), as an impurity element in copper and copper-based alloys, usually leads to intergranular embrittlement even at ppm concentrations. However, the intrinsic mechanisms of the embrittlement remain largely unclear. In this study, we systematically investigate the influence of trace amounts of S (53 and 300 wt ppm) on the ductility of an ultrahigh-purity copper (99.99999%) in the range of room temperature to 900 °C. Tensile results show an excellent plastic deformation capacity at any test temperature for the ultrahigh-purity copper, while a remarkable reduction in ductility for both S-containing alloys, particularly at 300–750 °C. A microanalysis reveals formation of micro- and nanoscale Cu–S precipitates, mainly distributed at grain boundaries, acting as the nucleation sites for small cavities leading to the crack initiation. This is responsible for the ductility loss in the S-containing alloys in the whole temperature range. The distinct embrittlement behavior between 300 and 750 °C is independent on the crystallographic orientation relationship between the Cu–S precipitates and Cu matrix, but is dominated by the temperature-dependent phase transition behavior of the Cu–S precipitates. Such a structural transformation with the volume expansion accelerates the nucleation and propagation of the microcracks, causing the intergranular embrittlement at intermediate temperatures. Our findings provide a comprehensive experimental understanding on the fundamental mechanisms of impurity-induced the embrittlement in metallic materials.

A Systematical Evaluation of the Crystallographic Orientation Relationship between MC Precipitates and Ferrite Matrix in HSLA Steels.

Here we systematically investigate the crystallographic orientation relationship (OR) between MC-type precipitates (M, metal; C, carbon) and ferrite matrix in the Ti-Mo microalloyed steel with different processing. In the specimens without austenite deformation, the interphase precipitation can be obtained, and the precipitates obey Baker–Nutting (BN) OR with ferrite matrix. By contrast, in the specimens with austenite deformation, the supersaturated precipitates were formed in ferrite grains, which can obey BN, Nishiyama–Wasserman (NW), Kurdjumov–Sachs (KS) and Pitsch (P) ORs simultaneously. The cooling rate after austenite deformation can influence the OR between carbides and ferrite in the MC/ferrite system. At the cooling rate of 80 °C/s, carbides and ferrite can roughly satisfy these OR with the deviation ≥ 10°, while at the cooling rate of 20 °C/s, carbides and ferrite can strictly obey the specific OR. The energy accumulated in the deformation process and maintained in the fast-cooling process (80 °C/s) can offset the formation energy of the carbides. Thus, the carbides formed in the specimen with the cooling rate of 80 °C/s do not strictly satisfy the specific ORs to meet the rule of lowest energy, and then deviate by a small angle based on the specific ORs.

Synthesis of ultrafine dual-phase structure in CrFeCoNiAl0.6 high entropy alloy via solid-state phase transformation during sub-rapid solidification

High entropy alloys (HEAs) with superb mechanical properties have been traditionally produced by solidification and subsequent heat treatment. In this paper, we demonstrate a new route via one-step process using sub-rapid cooling. Under proper cooling rates, the CrFeCoNiAl0.6 HEA could form ultrafine FCC+BCC dual-phase structure. By varying cooling rate, we can control the fraction of the BCC phase and refinement of FCC microstructures that have tunable mechanical properties in yield strength and hardness ranging from ∼580 to ∼1460 MPa and ∼260 to ∼550 Hv. We show that the structure-property-processing relation originates from the sideplate microstructures formed during fast cooling that have specific crystallographic orientation relationship between the FCC and BCC phases and chemical segregation. This work provides a new setting for better understanding of the solid-state phase transformation in HEAs under sub-rapid solidification conditions as well as a novel method for development of high-performance HEAs.

The Role of Parent Phase Topology in Double Young–Kurdjumow–Sachs Variant Selection during Phase Transformation in Low-Carbon Steels

The present paper investigates the role of parent phase topology on a crystallographic variant selection rule. This rule assumes that product phase nuclei appear at certain grain boundaries in the parent structure, such that a specific crystallographic orientation relationship is observed with both parent grains at either side of the grain boundary. The specific crystallographic orientation correspondence considered here is the Young–Kurdjumow–Sachs (YKS) orientation relationship &lt;112&gt;90° (which exhibits 24 symmetrical equivalents). The aforementioned relationship is characteristic of phase transformations in low-carbon steel grades. It is shown that, for different parent phase textures, ~20% of the grain boundaries comply with the double YKS condition allowing for a tolerance of 5°, ignoring the presence of topology in the parent phase microstructure. The presented model allows for connecting the presence of a specific parent phase topology with the condition of the double YKS variant selection rule in a number of practical cases: (i) for hot rolled Ti–Interstitial Free (IF) steel with and without Mn addition, (ii) for cold rolled IF steel exhibiting very strong texture memory after forward and reverse α ⇌ γ phase transformation and (iii) for a martensitic transformation in a Fe–8.5% Cr steel. It is shown that the double YKS variant selection criterion may explain several specific features of the observed transformation textures, while assuming a non-correlated arbitrary pair topology of the parent austenite structure (implying that for N parent orientations N/2 pairs are selected in an arbitrary manner).