Thin Laths Research Articles

Massive transformation in dual-laser powder bed fusion of Ti6Al4V alloys

In the present investigation, we fabricated additively manufactured Ti6Al4V parts using dual laser-powder bed fusion (DL-PBF) and identified the occurrence of a massive transformation. A detailed and systematic study of the massive transformation in the DL-PBF process by changing the energy and time offset of the lag laser beam and its effect on the microstructural and mechanical properties was undertaken. A mixture of martensite and massive phases was observed within the prior β grains in DL-PBF, and the dimensions of these massive grains increased with an increase in the lag laser beam energy, while acicular α′ martensite was present in the single Laser-PBF. The massive phase showed a featureless patch-shaped region, which consisted of thin laths, and they were associated with the prior β grain boundaries. The irregular patch-shaped regions showed inferior Vickers hardness when compared with acicular α′ martensite, and the ultimate tensile strength was lower in the DL-PBF than in the single Laser-PBF. The columnar prior-β grain was present in all the samples (both in the single- and dual-beam laser) and the dimensions of the grains varied with increasing the lag laser beam energy. These present results showed that the DL-PBF process significantly influenced the microstructural and mechanical properties of the Ti6Al4V materials, and provided a deep insight into massive phase transformation in AM titanium alloys and its effect on the mechanical properties.

Grain Refinement and Phase Transformation of Pure Titanium Foils During Asymmetrical Rolling

Ultrafine‐grained microstructure and face center cubic (FCC) phase are produced in the pure titanium foils through asymmetrical rolling (ASR) to explore the mechanical properties of pure titanium foils with different thicknesses. Herein, the grain refinement process and phase transformation behavior are systematically investigated. The grain refinement process can be described as: 1) coarse equiaxed grains are elongated along RD due to the compressive strain and shear strain caused by the ASR process. 2) elongated grains are split into thin laths and subgrains by dislocation walls under greater strain. 3) thin laths and subgrains are further refined and ultrafine‐grained microstructures are obtained. In addition, hexagonal close‐packed (HCP)‐FCC phase transformation is also discovered during the ASR process. The orientation relationship between the HCP and FCC phases is determined as [0001]HCP//[001]FCC, (100)HCP//(20)FCC and the phase transformation is caused by Shockley partial dislocation with Burgers vector 1/6[110] gliding on each (100) plane. Uniaxial tensile tests on heat‐treated pure titanium foils of different thicknesses show a size effect on tensile properties. As the thickness decreases, tensile strength and elongation are reduced, with fewer/single‐layer equiaxed grains at the section of the specimen.

Microstructural characteristics and mechanical properties of additively manufactured Cu–10Sn alloys by laser powder bed fusion

Cu – 10 wt% Sn (Cu–10Sn) alloy specimens were additively manufactured by varying the laser powder bed fusion (LBPF) processing parameters, e.g., laser power (200–350 W) and laser scan speed (100–1400 mm/s) at a fixed hatch spacing (0.12 mm) and slice thickness (0.03 mm), to examine their effects on the density, melt pool structure, and microstructure. Microstructural characteristics of the most dense sample were examined using electron microscopy (SEM, TEM) and X-ray Diffraction. The grains in the top-most melt pool layer showed a fan-like structure, whereas all other areas showed small columnar structure aligned nearly parallel to the build direction due to multiple melt-solidification cycles. The high cooling rates associated with LPBF yielded a fine dendritic microstructure, which consisted of primary α1(Cu) dendrites and a mixture of α2(Cu) and δ (Cu41Sn11) phases in the interdendritic region. In addition, formation of thin laths (∼120 nm) was observed by TEM presumably due to diffusionless martensitic transformation from the high temperature β phase associated with fast cooling rates. The primary α1(Cu) dendrite and α2(Cu) within the interdendritic region contained low (∼6.6 wt%) and high (∼11.9 wt%) Sn concentration, respectively. Mechanical properties in tension of the dense Cu–10Sn alloy was measured in as-built condition, i.e., σUTS = 564 MPa, σY = 387 MPa, El = 26%; these are significantly superior to the properties determined in previous LPBF investigations and as-cast Cu–10Sn alloy, most likely due to contributions from Hall-Petch and dislocation strengthening mechanisms. Solidification path in LPBF fabricated Cu–10Sn alloy was also revealed from an extensive TEM investigation.

Study on Mechanical Properties and Microstructure of the Ultrastrong Low Alloy Wear‐Resistant Steel

Herein, a kind of the ultrastrong low alloy wear‐resistant steel suitable for excavator bucket teeth is prepared. The ultrastrong steel with good toughness and wear resistance is successfully prepared by the forging, quenching, and tempering processes. The yield strength, tensile strength, elongation, and hardness of the ultrastrong steel reached up to 1700, 1960 MPa, 7%, and 563HV, respectively. Optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) are used to observe the microstructures of the ultrastrong steel. After the forging, quenching, and tempering, two types of martensite laths are formed in the matrix of the ultrastrong steel, i.e., the coarse laths with low‐density dislocations and the thin laths with high‐density dislocations and some ε‐carbides. Low‐temperature tempering allows the carbides to precipitate in large quantities, and maintains the matrix with high density dislocations in the thin laths, which is the micromechanism of the steel with high strength and high toughness, and good wear resistance.

Microstructure and Texture Evolution of Rolled Plate for Cu–15Cr In-Situ Composite

The microstructure and texture of different rolling processes in situ Cu–15Cr sheets are studied. The results show that the second phase Cr in the material gradually become broken, flattened, merged and homogenized from dendritic state to oriented thin lath. Meanwhile, the texture in distributed copper matrix grains finally forms Brass {110} , Goss {001} and Copper {112} textures along with Cr phase texture of randomly distributed α-fiber ( fiber) and γ-fiber ( fiber) texture. Based on VPSC (visco-plastic self-consistent model), the texture of cold rolled Cu–15Cr composite is simulated, and the simulation result indicates that obvious twinning effect in the copper matrix appears with a feature of a special texture evolution law of Goss.

Microstructural evolution and related mechanisms in NiTiCu shape memory alloy subjected local canning compression

The microstructural evolution and related mechanisms in NiTiCu shape memory alloy (SMA) subjected to severe plastic deformation (SPD) were investigated based on local canning compression. During the local canning compression, the NiTiCu SMA experiences four stages, which involve the elastic accommodation of martensite variants, the inelastic deformation process induced by martensite reorientation and detwinning, the elastic deformation of martensite phase and the plastic deformation of martensite phase. During the plastic deformation, dislocation slip is activated firstly, and then twinning deformation is induced to accommodate the further deformation. When the density of deformation twins reaches saturation state, shear bands are generated to accommodate the further increasing strain. Under the shear banding deformation, the twins in the shear bands are broken into fine-equiaxed grains accompanied with local amorphization. The new rounds of shear banding deformation result in the further grain refinement and the fraction increase of amorphous phase. The refined microstructures of the NiTiCu SMA are induced by two essential processes, which involve the formation of thin lath structures split from elongated laths and the breakdown of thin lath structures by transverse dislocation walls composed of high density of dislocations.

Microstructural evolution of equal channel angular drawn purity titanium at room temperature

Thin commercial-purity titanium (CP–Ti) wire was successfully acquired by equal channel angular drawing (ECAD) at room temperature with route Bc using a 90° die at a relatively high drawing speed of 10 mm s−1. The as-drawn CP–Ti wires were of good quality free of cracks and segmentation on their surface. The grain size of CP–Ti was reduced from ∼32 μm for the as-annealed wire to ∼700 nm for 12-passes equal channel angular drawn wire. The grain experienced transition from microband to thin lath and to equiaxed subgrains with the increment in drawing passes. Face-centered cubic (FCC) phase was triggered obviously to accommodate the large shear strain induced by ECAD at the drawing rate of 20 mms−1. The thickness of the FCC phase increased with an increase in drawing passes, and no equiaxed subgrains were formed in CP–Ti. Accordingly, the drawing speed significantly affects the deformation mode and microstructural evolution of CP–Ti during ECAD. A lower drawing speed provides a longer time for the structure recovery, thus resulting in the occurrence of dynamic recovery when ECAD was performed at room temperature. Additionally, {101¯2} tension twinning and {112¯2} compression twinning occurred simultaneously to accommodate ECAD shear deformation. The success in processing CP–Ti rods at room temperature through multiple passes of ECAD provides a new perspective to efficiently fabricate ultrafine grained small-sized materials continuously.

Grain refinement and phase transition of commercial pure zirconium processed by cold rolling

The grain refinement process and phase transition phenomena of a cold-rolled zirconium have been systematically investigated. The grain refinement was accomplished via a sequential series of dislocation behaviors, reaching a final grain size of <100nm. The refinement process can be described as: (1) dislocation nucleation, multiplication and tangling inside the original coarse-grains, (2) formation of microbands via dislocation rearrangement, (3) further division of microbands into thin laths, (4) split of microbands and thin laths into subgrains and then nanograins. Two different types of HCP-FCC phase transitions were also discovered during the cold rolling process, with the transition mechanisms and their influences on the mechanical properties being discussed.

Effects of cold rolling and subsequent annealing on the microstructure of a HfNbTaTiZr high-entropy alloy

Abstract

Phase transformation mechanisms in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy after subsequent annealing at 800 °C

During the processing of high Nb-containing TiAl (Nb-TiAl) alloys, the cooling rate at certain parts of the components can be very high, especially at thin parts. Moreover, annealing treatment must be applied to TiAl alloys to improve their mechanical properties. In this study, the phase transformation mechanisms in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy during subsequent annealing were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results show that βo, α2, and massively transformed γ phases co-exist in the as-quenched microstructure. Some fine γ laths nucleated in the primary α2 phase in the quenched samples. After annealing at 800 °C for 1 h, numerous extremely fine γ laths precipitated in the bulk α2 phase and could only be recognized using TEM imaging. The ωo particles at sizes of 0.5–1 μm precipitated in the retained βo phase and nearly consumed all of the βo areas. More interestingly, some coarsened γ grains in true-twin relationship were observed at the boundaries of the lamellar colony and βo(ω) regions. The orientation relationship between βo(ω) and coarsened γ was confirmed to be the following: [110]β//[112¯ 0]ω//[111]γ, (111¯)β//(0001)ω//(11¯ 0)γ. After annealing at 800 °C for 100 h, the βo phase region transformed into small ωo particles and equiaxed γ grains and still followed the above-mentioned orientation relationship. The α2 phase only existed as thin laths in the lamellar structures in a small volume fraction. These results indicate that the ωo phase is stable at 800 °C. Possible mechanisms of these phase transformations are discussed.

Change in coccolith size and morphology due to response to temperature and salinity in coccolithophore &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; (Haptophyta) isolated from the Bering and Chukchi seas

Abstract. Strains of the coccolithophore Emiliania huxleyi (Haptophyta) collected from the subarctic North Pacific and Arctic oceans in 2010 were established as clone cultures and have been maintained in the laboratory at 15 °C and 32 ‰ salinity. To study the physiological responses of coccolith formation to changes in temperature and salinity, growth experiments and morphometric investigations were performed on two strains, namely MR57N isolated from the northern Bering Sea and MR70N at the Chukchi Sea. This is the first report of a detailed morphometric and morphological investigation of Arctic Ocean coccolithophore strains. The specific growth rates at the logarithmic growth phases in both strains markedly increased as temperature was elevated from 5 to 20 °C, although coccolith productivity (estimated as the percentage of calcified cells) was similar at 10–20 % at all temperatures. On the other hand, the specific growth rate of MR70N was affected less by changes in salinity in the range 26–35 ‰, but the proportion of calcified cells decreased at high and low salinities. According to scanning electron microscopy (SEM) observations, coccolith morphotypes can be categorized into Type B/C on the basis of their biometrical parameters. The central area elements of coccoliths varied from thin lath type to well-calcified lath type when temperature was increased or salinity was decreased, and coccolith size decreased simultaneously. Coccolithophore cell size also decreased with increasing temperature, although the variation in cell size was slightly greater at the lower salinity level. This indicates that subarctic and arctic coccolithophore strains can survive in a wide range of seawater temperatures and at lower salinities with change in their morphology. Because all coccolith biometric parameters followed the scaling law, the decrease in coccolith size was caused simply by the reduced calcification. Taken together, our results suggest that calcification productivity may be used to predict future oceanic environmental conditions in the polar regions.

Grain refinement via formation and subdivision of microbands and thin laths structures in cold-rolled hafnium

The microstructural evolution and mechanical properties of pure hafnium subjected to cold rolling were investigated in this paper. Structural characterization indicates that slip dominated the plastic deformation and the microstructural evolution follows the sequence: original coarse grains – formation of microbands – formation of thin laths in microbands and formation of elongated grains in locally formed shear bands – the longitudinal splitting and transverse breakdown of laths to elongated segments – formation of nano-grains through further transverse breakdown of elongated segments. Hardness results indicate that strain hardening occurred during the whole rolling process, which can be attributed to dislocation activities and grain refinement effect.

An atomic study of the transitional region between γ/γ laths in γ-TiAl

In the present study, a transitional region between two thick γ laths is investigated with TEM, HAADF-STEM, EDX and HRTEM. The results show that the transitional region consists of three thinner γ laths, and all the thick and thin laths have a true twin relationship. The interface between γ/γ laths is basically a twin-related interface but involving a rigid body translation of the adjacent lamellae, and misfit compensating has been observed along the interface. Ti segregates into the transitional region, which is essential to formation of the three thin γ laths. Based on the characterization of the transitional region, the formation mechanism of the transitional region is revealed.

Microstructural Evolution of Martensite Phase in Fe-Ni Alloy Depending on Temperature of Tensile Deformation

Martensite (α’) formed in Fe-Ni alloy is mainly separated into four morphologies (thin plate, lenticular, butterfly and lath). The morphology of the α’ depends on its formation temperature because accommodation process for transformation strain in the α’ is changed with temperature. Also, crystal orientation relationship between α’ and austenite (γ) is depended on the morphology of the α’. In this study, temperature dependence of the microstructural evolution of the butterfly-type α’ in Fe-30mass%Ni alloy by tensile deformation is investigated. When the tensile test is performed at room temperature (RT), morphology of the butterfly-type gets close to lath-type α’. On the other hand, the morphology of the butterfly-type α’ is kept under the tensile test at lower temperature. These microstructural changes of the butterfly-type α’ depending on the tensile temperature are discussed in term of the change of the accommodation process for the transformation strain.

Effect of Rare Earths and Vanadium on Microstructure and Mechanical Properties of High Chromium Cast Iron

Effect of RE and V on microstructure and mechanical properties of high chromium cast iron were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, impact test and wear test. The results show that proper modification using RE combined with V makes the alloy present a more refined and homogenous austenite matrix, and makes the morphology of carbide changing from thick lath to thin lath, and rosette-like. Modification can also increase hardness, wear resistance and impact toughness of high chromium cast iron.

Synthesis, characterization and X-ray crystal structures of two polymorphs of a cobalt(III) complex with a N3O2 pentadentate Schiff base ligand, and benzylamine: spectral and electrochemical studies

The title complex [CoIII{(naph)2dpt}(bzlan)]BPh4, where (naph)2dpt stands for bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriamine dianion and bzlan for benzylamine, has been synthesized and characterized by elemental analyses, IR, UV–Vis and 1H NMR spectroscopy. The structures of two possibly concomitant polymorphs, obtained from methanolic solution, [polymorph I (monoclinic, centrosymmetric, red-brown, thickish prismatic platelets) and polymorph II (orthorhombic, noncentrosymmetric, ochre olive-green, thin laths)] have been determined by X-ray crystallography. The geometry around the central cobalt ion is distorted octahedral in both polymorphs, but the benzylamine shows different kinds of orientation and disorder.

Blue Intensity In Pinus sylvestris Tree Rings: A Manual for A New Palaeoclimate Proxy

Minimum blue intensity is a reflected light imaging technique that provides an inexpensive, robust and reliable surrogate for maximum latewood density. In this application it was found that temperature reconstructions from resin-extracted samples of Pinus sylvestris (L.) from Fennoscandia provide results equivalent to conventional x-ray densitometry. This paper describes the implementation of the blue intensity method using commercially available software and a flat-bed scanner. A calibration procedure is presented that permits results obtained by different laboratories, or using different scanners, to be compared. In addition, the use of carefully prepared and chemically treated 10-mm-diameter cores are explored; suggesting that it may not be necessary to produce thin laths with the rings aligned exactly perpendicular to the measurement surface.

Microstructure evolution and nanograin formation during shear localization in cold-rolled titanium

The microstructure evolution within the shear localization areas formed in commercial titanium subjected to cold rolling is systematically investigated. Sheared micro-regions are first initiated followed by the formation of distinct microscopic shear bands, which gradually grow and coalesce to form a macroscopic shear band. The latter contains thin lath structures in the boundary regions, fine elongated subgrains in the outer areas and roughly equiaxed (sub)grains with a mean size of 70 nm in the centre region. The early stage of shear localization involves the formation of twin/matrix lamellae aligned along the shear direction. The lamellae subsequently undergo longitudinal splitting into thin laths, which are in turn subjected to transverse breakdown, giving rise to fine elongated subgrains. The continuing thermally assisted lath breakdown, in conjunction with lateral sliding and lattice rotations, ultimately leads to the formation of roughly equiaxed, nanosized (sub)grains in the macroscopic shear band centre at large strains.

Meurigite-Na, a new species, and the relationship between phosphofibrite and meurigite

The new mineral meurigite-Na, [Na(H 2 O) 2.5 ][Fe 8 3+ (PO 4 ) 6 (OH) 7 (H 2 O) 4 ], is monoclinic with space group C 2/ c and cell parameters a = 28.835(2), b = 5.1848(4), c = 19.484(1) A, β = 106.983(6)°, V = 2785.8(2) A 3 , and Z = 4. It is the Na analog of meurigite, which is now named meurigite-K. The type locality of meurigite-Na is the Silver Coin mine, Valmy, Iron Point district, Nevada, where it occurs as radial sprays of cream-colored, flattened fibers (thin laths) to 0.4 mm in length. At the Silver Coin mine, meurigite-Na occurs very late in a paragenetic sequence that includes (in approximate order from early to late) quartz, barite, apatite-(CaF), goethite, rockbridgeite, cacoxenite, alunite, wardite, turquoise/chalcosiderite, leucophosphite, lipscombite/zinclipscombite, kidwellite, strengite/variscite, crandallite/perhamite, and jarosite. Meurigite-Na also occurs at Tom’s quarry and Moculta quarry in South Australia, Australia, Lake Boga quarry and probably Rixon’s Sandstone quarry in Victoria, Australia, and at an unnamed pegmatite prospect near Linopolis, Minas Gerais, Brazil. The streak is white, the luster is silky, and the Mohs hardness is about 3. The measured density is 2.94(2) g/cm 3 and the calculated density is 2.954 g/cm 3 . Optical properties: biaxial (−), α = 1.740(3), β = 1.759(3), γ = 1.763(3), 2 V meas = 50(10)°; X ≅ c , Z = b . The strongest powder X-ray diffraction lines are [ d ( hkl ) I ]: 13.8(200)20, 9.35(002)100, 4.843(111)20, 3.206(712)40, 3.107(713)30, 2.971(513)15, and 2.593(116)15. Meurigite-Na is insoluble in concentrated HCl. Evaluation of powder XRD and chemical-analytical data in light of the structure determination for meurigite-K leads to the conclusion that type phosphofibrite is isostructural with meurigite and represents the alkali-deficient member of a series with meurigite-K.

Effects of Rare Earths and Al on Structure and Performance of High Chromium Cast Iron Containing Wolfram

Effects of RE and Al on the structure, impact toughness, hardness, and wear resistance of high chromium cast iron containing wolfram were investigated. The results show that without modification the volume fraction of austenite is high and the carbide appears to be thick lath and the grain size is relatively large; proper modification using RE combined with Al can reduce volume fraction of residual austenite in the as-cast structure obviously, refine grain size of primary austenite notably, and make the morphology of carbide changing from thick lath to thin lath, rosette, and feather-like modification can also increase hardness, wear resistance and impact toughness of cast iron.