Effect Of Microstructural Anisotropy Research Articles

Effect of Microstructural Anisotropy on Fracture Toughness of Selective‐Laser‐Melted 15‐5 PH Stainless Steel

Herein, the influence of microstructure anisotropy on fracture toughness of selective laser melting‐fabricated and directly aged 15‐5 PH stainless steel is investigated. A bimodal columnar (within the melt pool) and equiaxed (at the melt pool boundary) microstructure forms on the vertical plane, which results in a higher yield strength in the horizontal direction than the vertical direction. For fracture toughness, the value is 10% higher in the specimen with the crack propagation perpendicular to the build direction than parallel to the build direction. The main cause for such an anisotropic fracture toughness is related to the circuitous crack path along the melt pool boundary when the crack propagation is perpendicular to the build direction.

Effect of Microstructural Anisotropy on Corrosion Resistance of 316L Stainless Steel Prepared by Additive Manufacturing

Effect of Microstructural Anisotropy on Corrosion Resistance of 316L Stainless Steel Prepared by Additive Manufacturing

Anisotropy and variability in thermal creep behaviour of Zr-2.5Nb pressure tube

The Zr-2.5Nb alloy pressure tubes of Indian Pressurized Heavy Water Reactors were manufactured from double melted ingots initially and subsequently from quadruple melted ingots to reduce impurities such as chlorine, phosphorus and carbon. In the current investigation, creep tests were carried out in the stress range of 0.7–0.9 times the yield strength and the temperature range of 350 °C–450 °C to characterize the thermal creep behaviour of Zr-2.5Nb alloy pressure tubes fabricated from double and quadruple melted ingots. The rupture time, minimum creep rate, stress exponent, activation energy and threshold stresses were obtained by carrying out the creep tests of the samples fabricated with their axis parallel to the axial and transverse directions of the pressure tubes. Experimental analysis revealed that the rupture time for double melted tube was 2–3 times lower than that of quadruple melted tubes, whereas no significant change in minimum creep rate was observed. Stress exponent values were obtained in the range of 3–5 signifying dislocation creep as the dominant creep mechanism. To predict the long-term creep properties, the master curves employing the Larson-Miller and Monkman-Grant methods were also evaluated. The effect of microstructural anisotropy, alloying elements and impurities on the thermal creep behaviour of Zr-2.5Nb pressure tube has been investigated.

Effect of microstructure induced anisotropy on fatigue behaviour of functionally graded Inconel 718 fabricated by additive manufacturing

In this paper, the effect of microstructural anisotropy on the fatigue crack growth behaviour of the functionally graded Inconel 718 fabricated through laser powder bed fusion (L-PBF) is investigated. Different manufacturing parameters, including low and high laser powers, were used to produce a variety of non-graded (NG) and functionally graded (G) specimens in two build directions, vertical and horizontal. In addition, a group of heat treated wrought samples was tested as a reference. It was observed that the different manufacturing parameters result in various grain size, crystallographic textures, precipitates and Laves phases, porosity, and un-melted particles. Three-point bending fatigue tests were conducted to measure the threshold stress intensity factor (ΔK th ) and fatigue crack growth rate (FCGR),da/dN. Only the lower laser power L-BPF Inconel material was found to have comparable to the wrought heat treated material fatigue crack growth behaviour. Furthermore, a new approach of automatically controlling ΔK as a function of the crack length was employed for graded specimens to investigate the crack growth rate as a function of local microstructure. The FCGR value of the vertical L-PBF samples, in which the crack direction was perpendicular to the build direction, remained constant. In contrast, the da/dN value of the horizontal samples with the crack direction parallel to the build direction increased constantly with the increase of the crack length. This behaviour is in good agreement with the hardness profile of the graded materials. Melt pool boundaries, graded interface boundaries, and grain orientations close to 〈001〉 were found to deflect the crack path. Additionally, it was found that L-PBF material is more affected (at a low stress ratio of R = 0.1) by the roughness-induced crack closure than the wrought counterparts. This study has successfully demonstrated the feasibility of using an additive manufacturing process to fabricate functionally graded materials featuring tailorable fatigue response of the local microstructures. • The hardness profiles of the functionally graded materials found to be highly affected by the build direction. • The Non-graded lower laser power material showed a comparable fatigue crack growth behaviour to the wrought material at a low stress ratio of R = 0.1. • The fatigue crack growth rate of the functionally graded materials along the crack length found to be almost constant for the V samples while it had an increasing trend for the H samples.

Effect of microstructural anisotropy on severe plastic deformation during material removal at micrometer length-scales

The emergence of shear inhomogeneity across grain boundaries during severe shear deformation in Cu at the micrometer length-scales is demonstrated through in situ imaging inside a scanning electron microscope. The deformation mechanics during machining is found to be orientation dependent. Microstructure refinement from severe plastic deformation in confined volumes is entirely suppressed in certain orientations but results in a characteristic ultrafine structure in others. Rampant ductile fracture is found to nucleate at some grain boundaries due to elevated dislocation densities, and this failure mechanism is imprinted on the freshly generated surface, which limits the precision of machining-based processes (e.g., diamond turning) in nanometrically-smooth roughness profiles.

Effect of microstructural anisotropy on fracture toughness of hot rolled 13Cr ODS steel – The role of primary and secondary cracking

ODS steels have been known to exhibit anisotropic fracture behaviour and form secondary cracks. In this work, the factors responsible for the anisotropic fracture behaviour have been investigated using scanning electron microscopy and electron backscatter microscopy. Fracture toughness of hot rolled 13Cr ODS steel was determined using unloading compliance method for L-T and T-L orientations at various temperatures. L-T orientation had higher fracture toughness than T-L orientation and also contained more pronounced secondary cracking. Secondary cracks appeared at lower loads than primary cracks in both orientations. Primary crack propagation was found to be preferentially through fine grains in a bimodal microstructure. Grains were aligned and elongated the most towards rolling direction followed by T and S directions resulting in fracture anisotropy. Crystallographic texture and preferential alignment of Ti enriched particles parallel to rolling direction also contributed towards fracture anisotropy.

Effect of microstructural anisotropy on the mechanical properties of K-doped tungsten rods for plasma facing components

The effect of microstructural anisotropy in pure tungsten (W) and potassium (K) doped W rods (20mm in diameter) on their mechanical properties was investigated by tensile tests along the axial and radial directions at temperatures from 473K to 1573K and fracture analysis. K-doping led to improved tensile strength regardless of the test direction and temperature. K-doping did not alter the elongation regardless of the test direction in the temperature range showing ductile fracture. The ductility at lower temperature range was improved by the K-doping, especially in tensile tests along the radial direction. The lowest temperature of ductile fracture along both axial and radial directions decreased from 1373K to 973K because of K-doping. Thus, K-doping could suppress the influence of microstructural anisotropy on tensile properties, especially ductility, in large diameter W rods.

Mechanical characterization of GdBCO/Ag and YBCO single grains fabricated by top-seeded melt growth at 77 and 300 K

YBaCuO and GdBaCuO + 15 wt% Ag large, single-grain, bulk superconductors have been fabricated via the top-seeded, melt-growth (TSMG) process using a generic NdBCO seed. The mechanical behavior of both materials has been investigated by means of three-point bending (TPB) and transversal tensile tests at 77 and 300 K. The strength, fracture toughness and hardness of the samples were studied for two directions of applied load to obtain comprehensive information about the effect of microstructural anisotropy on the macroscopic and microscopic mechanical properties of these technologically important materials. Splitting (Brazilian) tests were carried out on as-melt-processed cylindrical samples following a standard oxygenation process and with the load applied parallel to the growth-facet lines characteristic of the TSMG process. In addition, the elastic modulus of each material was measured by three different techniques and related to the microstructure of each sample using optical microscopy. The results show that both the mechanical properties and the elastic modulus of both YBCO and GdBCP/Ag are improved at 77 K. However, the GdBCO/Ag samples are less anisotropic and exhibit better mechanical behavior due to the presence of silver particles in the bulk, superconducting matrix. The splitting tensile strength was determined at 77 K and both materials were found to exhibit similar behavior, independently of their differences in microstructure.

Effect of Microstructural Anisotropy of PM Precursors on the Characteristic Expansion of Aluminum Foams

This work investigates the causes of the anisotropic early expansion (below the melting point) of powder metallurgical (PM) aluminum foam precursors by evaluating the crystallographic anisotropy induced during the production of the precursor materials. A varied group of precursors prepared using different parameters and techniques (direct powder extrusion and hot uniaxial compression) has been investigated. Multidirectional foaming expansion has been registered in situ by means of the optical expandometry technique, while X-ray diffraction has been used to characterize the preferred crystallographic orientation (texture) of the pressed powders. The results point to a clear correlation between the expansion anisotropy and the microstructural crystallographic anisotropy of the precursors. Although this correlation is not a direct cause–effect phenomenon, it is a good indicator of intrinsic precursor characteristics, such as densification and powder interparticle bonding, which govern the expansion behavior during the early stages when the material is still in a solid or semisolid state.

Effect of microstructural anisotropy on the fluid–particle drag force and the stability of the uniformly fluidized state

AbstractLattice-Boltzmann simulations of fluid flow through sheared assemblies of monodisperse spherical particles have been performed. The friction coefficient tensor extracted from these simulations is found to become progressively more anisotropic with increasing Péclet number, $Pe= \dot {\gamma } {d}^{2} / D$, where $\dot {\gamma } $ is the shear rate, $d$ is the particle diameter, and $D$ is the particle self-diffusivity. A model is presented for the anisotropic friction coefficient, and the model constants are related to changes in the particle microstructure. Linear stability analysis of the two-fluid model equations including the anisotropic drag force model developed in the present study reveals that the uniformly fluidized state of low Reynolds number suspensions is most unstable to mixed mode disturbances that take the form of vertically travelling waves having both vertical and transverse structures. As the Stokes number increases, the transverse-to-vertical wavenumber ratio decreases towards zero; i.e. the transverse structure becomes progressively less prominent. Fully nonlinear two-fluid model simulations of moderate to high Stokes number suspensions reveal that the anisotropic drag model leads to coarser gas–particle flow structures than the isotropic drag model.

Effect of microstructural anisotropy on stress corrosion cracking of hot rolled duplex stainless steels

Anisotropy in stress corrosion cracking of lean grade UNS S32101 and standard grade UNS S32205 hot rolled duplex stainless steels was evaluated in this study. Microstructures were characterised with stereology methods in three orthogonal orientations to quantify anisotropy in phase distribution. Constant extension rate tests were conducted in an autoclave at 2×10−6 s−1 in chloride containing alkaline sulphide solution at 170°C. The maximum crack lengths and average crack densities were measured for the rolling longitudinal and transverse longitudinal orientations after stress corrosion cracking tests. Results indicate that stress corrosion crack initiation and growth are a strong function of the microstructure in each orientation. Maximum crack length and average crack density were maximum for the rolling longitudinal orientation. Crack initiation and growth were favoured along the transverse direction. Chlorides enhanced anisotropy in crack growth behaviour by facilitating crack initiation and crack coalescence along phase boundaries, which lead to more severe stress corrosion cracking in the alkaline sulphide environments that were studied.

Effect of Microstructural Anisotropy on Mechanical Behavior of a High-Strength Al–Mg–Si Alloy

The mechanical behavior of an extruded aluminum alloy pipe has been investigated after repeated failures in an oil and gas industry. The pipe failures occurred by longitudinal cracking, and the mechanical properties of the pipe were blamed for the failure. The relevant critical properties of the pipe including basic tests of hardness, tensile, and impact behavior were measured, and extended fatigue testing of the material was conducted. Microstructural examination revealed a recrystallized grain structure and clusters of constituent particles aligned in the direction of extrusion. Tensile testing in both the longitudinal and circumferential directions showed virtually identical yield and tensile strengths. However, the material exhibited higher toughness in the longitudinal direction. Impact test showed that the energy absorbed during fracture was four times higher in the longitudinal direction. Fatigue testing displayed a shorter fatigue life in the transverse direction. The study showed that the microstructure after extrusion and the distribution of the constituent particles have a pronounced effect on the mechanical behavior of the extruded pipe and induced anisotropy in the material performance. Performance of the material can be improved by choosing the proper extrusion ratio to control the microstructure and by controlling the density and distribution of the constituent particles.

Effect of Microstructure of Silicon Nitride Ceramics on Wear Mechanism

A silicon nitride sintered body with uni-directionally aligned β-Si3N4 elongated grains (UA-SN) was fabricated and the effect of microstructural anisotropy on wear properties was investigated. Block-on-Ring tests without lubricants were carried out using the UA-SN as block specimens and commercially supplied Si3N4 as ring specimens. In addition, scratch tests were also carried out using a diamond stylus having 25μm of tip radius with the normal load increasing continuously up to 1.47N. For UA-SN, tribological properties were evaluated in three directions with respect to the grain alignment; in the direction normal to the grain alignment on the plane normal to the grain alignment (N), and in the direction parallel (L) to and perpendicular (T) to the grain alignment in the side plane. The N direction exhibited the highest wear resistance, and the worn surface of this plane was quite smooth, in contrast to the other specimens whose surfaces were irregular owing to grain removing. For the scratch test, there was an inflexion point in friction force during increasing load for each specimen. The starting states of wear, such as grain removing, were observed at this point and the loads at this point among specimens correlated with the result of wear resistance obtained from wear tests. Microfracture of the silicon nitride induced by scratching started at the grain boundary as microcracks. Wear was caused by subsequent grain removing following propagation and combination of these microcracks. It is suggested that the high wear resistance achieved in the plane normal to the grain alignment is attributable to the inhibition of crack propagation along the sliding surface by the stacked elongated grains normal to the sliding surface.