Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.     

Starch consolidation of M3/2 high speed steel powder – influence of microstructure on mechanical properties

Abstract

The influence of microstructure on the mechanical properties of starch consolidated super solidus liquid phase sintered AISI type M3/2 high speed steel powder has been evaluated. Hardness measurements, Rockwell C indentation and scratch testing were used to evaluate the mechanical properties and light optical microscopy and scanning electron microscopy were used for post-test characterisation. The results show that it is possible to starch consolidate and sinter large particle size high speed steel powder to obtain microstructures with high mechanical strength. However, the results show a strong correlation between the as sintered microstructure and the resulting mechanical properties and illuminate the importance of having a dense and isotropic microstructure in order to meet engineering requirements in demanding applications. Consequently, the failure mechanisms observed during indentation and scratch testing can be related to residual pores, present in the low temperature sintered samples, and a coarse microstructure with eutectic carbides, present in the high temperature sintered samples.     

Experimental and numerical study of ball indentation for evaluation of mechanical properties and fracture toughness of structural steel

Determination of mechanical properties of materials using non-conventional techniques has been an active area of research for a long time. Among various small specimen techniques to determine mechanical properties of materials, the ball indentation technique (BIT) has proved to be advantageous. BIT is used to measure material’s mechanical properties including fracture toughness when a tensile test cannot be performed: on welded joints or critical locations of components under service. The present work highlights the applicability of BIT for evaluating flow behaviour of engineering structural steels En24. Standard mechanical properties like ultimate tensile strength, yield stress, strain hardening coefficient evaluated for steels with varying microstructures generated through heat treatment. To determine fracture toughness from the flow behaviour, non linear damage models have been utilized. Using this model, fracture toughness of the En24 steel at different heat treated conditions has been computed using the results generated by the BIT. These results are verified with the already established correlation in literature. Numerical validation of the results generated by the BIT has been carried out by Finite Element Modelling (FEM) using standard ABAQUS software package. The FE model of the BI simulation helps to compute sub indenter stress-strain fields which determine the extent of pile-up in highly ductile materials.     

Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

In this study, an attempt has been made to synthesize 1.0 wt pct nano-Y₂O₃-dispersed ferritic alloys with nominal compositions: 83.0 Fe-13.5 Cr-2.0 Al-0.5 Ti (alloy A), 79.0 Fe-17.5 Cr-2.0 Al-0.5 Ti (alloy B), 75.0 Fe-21.5 Cr-2.0 Al-0.5 Ti (alloy C), and 71.0 Fe-25.5 Cr-2.0 Al-0.5 Ti (alloy D) steels (all in wt pct) by solid-state mechanical alloying route and consolidation the milled powder by high-pressure sintering at 873 K, 1073 K, and 1273 K (600°C, 800°C, and 1000°C) using 8 GPa uniaxial pressure for 3 minutes. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young’s modulus, and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (from 1150 to 2550 MPa), Young’s modulus (from 200 to 240 GPa), indentation fracture toughness (from 3.6 to 15.4 MPa√m), and hardness (from13.5 to 18.5 GPa) and measure up to 1.5 through 2 times greater strength but with a lower density (~7.4 Mg/m³) than other oxide dispersion-strengthened ferritic steels (<1200 MPa) or tungsten-based alloys (<2200 MPa). Besides superior mechanical strength, the novelty of these alloys lies in the unique microstructure comprising uniform distribution of either nanometric (~10 nm) oxide (Y₂Ti₂O₇/Y₂TiO₅ or un-reacted Y₂O₃) or intermetallic (Fe₁₁TiY and Al_9.22Cr_2.78Y) particles' ferritic matrix useful for grain boundary pinning and creep resistance.     

Microstructure Development,Nanomechanical, and Dynamic Compression Properties of Spark Plasma Sintered TiB2-Ti-Based Homogeneous and Bi-layered Composites

The growing threats due to increased use of small-caliber armor piercing projectiles demand the development of new light-weight body armor materials. In this context, TiB₂ appears to be a promising ceramic material. However, poor sinterability and low fracture toughness remain two major issues for TiB₂. In order to address these issues together, Ti as a sinter-aid is used to develop TiB₂-(x wt pct Ti), (x = 10, 20) homogeneous composites and a bi-layered composite (BLC) with each layer having Ti content of 10 and 20 wt pct. The present study uniquely demonstrates the efficacy of two-stage spark plasma sintering route to develop dense TiB₂-Ti composites with an excellent combination of nanoscale hardness (~36 GPa) and indentation fracture toughness (~12 MPa m^1/2). In case of BLC, these properties are not compromised w.r.t. homogeneous composites, suggesting the retention of baseline material properties even in the bi-layer design due to optimal relief of residual stresses. The better indentation toughness of TiB₂-(10 wt pct Ti) and TiB₂-(20 wt pct Ti) composites can be attributed to the observed crack deflection/arrest, indicating better damage tolerance. Transmission electron microscope investigation reveals the presence of dense dislocation networks and deformation twins in α-Ti at the grain boundaries and triple pockets, surrounded by TiB₂ grains. The dynamic strength of around 4 GPa has been measured using Split Hopkinson Pressure Bar tests in a reproducible manner at strain rates of the order of 600 s^?1. The damage progression under high strain rate has been investigated by acquiring real time images for the entire test duration using ultra-high speed imaging. An attempt has been made to establish microstructure-property correlation and a simple analysis based on Mohr–Coulomb theory is used to rationalize the measured strength properties.     

The influence of microstructure on mechanical properties in Ti-3AI-8V-6Cr-4Mo-4Zr (Beta-C)

The effect of microstructure on mechanical properties of a metastable beta titanium alloy has been investigated, with emphasis on the influence of α-phase precipitation on tensile strength and ductility. A commercial alloy, Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-C) has been aged to produce both Type la (obeying the Burgers orientation relation) and Type 2α (not obeying the Burgers relation) as hardening precipitates in the beta matrix. Although a direct comparison of Types 1 and 2α could not be made, there did not seem to be any direct correlation between precipitate type and mechanical properties. Rather, it has been found that overaging to produce a coarse distribution of relatively large (>1000Å) noncoherent α precipitates provides the best combination of strength and duc-tility. The same strength can be achieved with a much finer distribution of small (～100-200A) coherent α precipitates, but with much reduced ductility.     

Comparative Evaluations and Microstructure: Mechanical Property Relations of Sintered Silicon Carbide Consolidated by Various Techniques

A comparative evaluation between pressureless or self-sintered silicon carbide (SSiC), hot-pressed silicon carbide (HP-SiC), and spark plasma-sintered silicon carbide (SPS-SiC) has been carried out with emphasis on examination of their microstructures and mechanical properties. The effect of sample dimensions on density and properties of SPS-SiC has been also examined. Elastic modulus, flexural strength, and fracture toughness measured by indentation or testing of single-edge notched beam specimens have been found to follow the following trend, HP-SiC > SSiC > SPS-SiC. The SPS-SiC samples have shown size-dependent densification and mechanical properties, with the smaller sample exhibiting superior properties. The mechanical properties of sintered SiC samples appear to be influenced by relative density, grain size, and morphology, as well as the existence of intergranular glassy phase. Studies of fracture surface morphologies have revealed the mechanism of failure to be transgranular in SSiC or HP-SiC, and intergranular in case of SPS-SiC, indicating the dominating influence of grain size and α-SiC formation with high aspect ratio.     

Characterization Method of Mechanical Properties of Dissimilar Steel Resistance Plug Welding Joints

A novel resistance plug welding process has wide prospects for dissimilar steel. However, until present, there is no effective method to characterize the mechanical properties of resistance plug welding joints. In this paper, the influence factors such as diameter of filler, diameter of surface plastic ring, and diameter of nugget were first used for analysis. Slug ratio and indentation depth (height) ratio were designed to characterize the mechanical properties of the resistance plug welding joints. The results show that smaller the slug ratio, better the mechanical properties of the joint. The tensile shear load of the joint is higher when the indentation depth (height) ratio is 92–102%, and the joint has the best tensile shear load when the indentation depth (height) ratio is 96% or 97% in this study. Slug ratio and indentation depth (height) ratio are suitable for characterizing mechanical properties of dissimilar steel resistance plug welding joints.     

Mechanical properties and wear behaviour of PM aluminium composite reinforced with (Fe3Al) particles

Abstract

Mechanical properties and wear behaviour of an aluminium matrix composite reinforced with Fe₃Al intermetallics have been studied. A 2014 alloy manufactured through mechanical alloying was used as the matrix. Three different Fe₃Al intermetallics have been used as reinforcement, also manufactured through mechanical alloying. The difference between them was the different mechanical alloying times (5 and 20 h were used) and the possibility of carrying out a heat treatment at 1000°C (on the 20 h milled intermetallic) before admixing to the aluminium matrix. The processing of these composite materials included mixing and cold compacting (conventional powder metallurgy) followed by hot extrusion (without caning and degassing). The effect of a T6 heat treatment was also evaluated. The influence of intermetallic additions on the mechanical properties (hardness and tensile strength) and wear behaviour (pin on disk test) was established. All intermetallics showed a good link with the matrix, and high reactivity with it during the heat treatment, as the microstructural study supports.     

Tension characteristics of notched specimens for Al-Li-Cu-Zr alloy sheets with various cerium contents

In the present article, the high strength Al-Li-Cu-Zr alloy sheets modified by a rare earth element, Ce, are considered for possible application in practical aircraft products containing structural notches or stress concentrations; accordingly, a study has been made on the effects of stress concentration levels and Ce contents on the tension strength of notched specimens for the alloy sheets. Moreover, a discussion has been set off on the theoretical predictability on the basis of a theoretical expression for the notch strength by means of the mechanical properties of the smooth specimens. The test results show that when the stress concentration level increases, the notch strength linearly decreases in the double logarithmic coordinate; by comparison with the Ce-free alloy, the Ce-containing alloy sheets exhibit an insignificantly varying notch strength when the Ce content changes from 0.13 to 0.31 wt pct in the transverse orientation specimens or is 0.21 wt pct in the longitudinal orientation specimens even though their ductility for the smooth specimens can be improved to a certain degree by the Ce modification. The test data of notched specimens under the theoretical stress concentration factor (K _t), from 2.0 to 8.0 agree better with the predicted values of notch strength. Therefore, in accordance with some engineering properties such as the ultimate tensile strength (UTS), percentage elongation (EL), and Young’s modulus (E) of the smooth specimens, the notch strength of the alloy sheets under plane strain state can be easily estimated in a certain range of stress concentration levels.     

Mechanical Properties of a Ni–Cr–Mo Steel Subjected to Room Temperature Carburizing Using Surface Mechano-Chemical Carburizing Treatment (SMCT)

Surface mechano-chemical carburizing treatment (SMCT) is a modified version of surface mechanical attrition treatment and it is one of the cutting-edge technologies for producing hard nano-crystalline surface in metallic materials. In the present study, a case carburized surface layer is achieved in 1.75 Ni–Cr–Mo steel at room temperature using SMCT. Activated charcoal powder is continuously fed during the process so as to achieve the carbon diffusion into the surface layer. The SMCT process has been carried out for different periods say 15, 30, 45 and 60 min respectively. The microstructure and surface chemical composition is investigated by using TEM and XRF analysis. The mechanical properties such as yield strength (YS), ultimate tensile strength (UTS), fracture toughness and surface hardness of SMCT samples have been investigated using universal testing machine, Plain strain fracture toughness test and Microvickers hardness test respectively. The surface carbon content has been found to increase linearly and grain size reduces continuously with processing time. A 60 min SMCT samples reveal 0.8% C and about 10 nm grains over the surface. The SMCT samples show significant improvement in mechanical properties. The surface hardness increases from 180 HV_0.1 to ~ 878 HV_0.1 by 60 min of treatment. About 55% increment in the YS and 30% increment in UTS is achieved by 60 min of SMCT. It is also interesting to note that the fracture toughness of the samples enhances from 24 to 47 MPa \( \sqrt m \) after 60 min of SMCT.     

7075铝合金化学镀对镍磷合金镀膜组织和性能的影响

金属表面处理直接影响7075铝合金的力学性能及耐腐蚀性能.以7075-T6铝合金为基体,采用化学镀(EN)技术在光滑基体表面均匀镀覆一定厚度的镍磷(Ni-P)镀膜,镀膜厚度分别为3.64、5.87和7.33 μm,并通过扫描电子显微镜(SEM)、X射线衍射(XRD)、硬度测试及电化学工作站等手段分析膜层特性及膜厚对70...     

Ball-indentation test technique for evaluating thermal and creep damage of modified 9Cr-1Mo steel

The Ball-Indentation (BI) testing based on multiple cycles of loading-unloading using a spherical indenter is a useful technique for evaluating tensile properties from a very small volume of material. In this study, the BI technique has been used in a novel way to evaluate the changes in mechanical properties of Modified (Mod) 9Cr-1Mo caused by creep exposures. Microstructural degradation of varying degrees in Mod 9Cr-1Mo steel is simulated by conventional creep test terminated at various strains. By carrying out BI tests on unstressed head and stressed gage portions of the creep specimens, the changes in the strength and ductility are evaluated. Microstructural evolution in the creep exposed conditions studied using transmission electron microscopy is related to the strength changes caused by the stressed exposures.     

Effects of Binder on the Properties of Iron Ore-Coal Composite Pellets

Large amounts of fines and superfines are generated in Indian iron ore and coal mines due to mechanized mining and mineral dressing operations. Utilization of these fines for extracting metal is of vital concern for resource utilization and pollution control. For agglomeration of these fines, a suitable binder is required. Iron ore-coal composite pellets were prepared by cold bonding. Various binders such as lime, Ca(OH)₂, slaked lime, dextrose, molasses, and sodium polyacrylate (SPA), alone or in combination, were employed for making composite briquettes. The slaked lime–dextrose combination produced the highest strength among the various binders employed for producing composite briquettes and was therefore selected for producing composite pellets for the smelting reduction. In cold bonding, the composite pellets attain the requisite properties due to physico-chemical changes of the binder in ambient conditions. It was possible to obtain a dry strength of more than 300 N per pellet in some cases and more than 200 N per pellet in many trials. Drop strength and shatter index values of composite pellets were also measured. In the present paper an attempt has been made to evaluate the mechanical properties of cold-bonded composite pellets so as to throw some light on the capacity of these pellets to withstand stresses during handling and transportation.     

Deterioration in Fracture Toughness of 304LN Austenitic Stainless Steel Due to Sensitization

The aim of this report is to examine the influence of sensitization on the mechanical properties of AISI grade 304LN stainless steel with special emphasis on its fracture toughness. A series of stainless steel samples has been sensitized by holding at 1023 K for different time periods ranging from 1 to 100 hours followed by water quenching. The degree of sensitization (DOS) for each type of the varyingly heat-treated samples has been measured by an electrochemical potentiodynamic reactivation (EPR) test. The microstructures of these samples have been characterized by optical metallography, scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses, together with measurements of their hardness and tensile properties. The fracture toughness of the samples has been measured by the ball indentation (BI) technique and the results are validated by conducting conventional J-integral tests. It is revealed for the first time that the fracture toughness and ductility of AISI 304LN stainless steel deteriorate significantly with increased DOS, while the tensile strength (TS) values remain almost unaltered. The results have been critically discussed in terms of the depletion of solid solution strengtheners, the nature of the grain boundary precipitations, and the strain-induced martensite formation with the increasing DOS of the 304LN stainless steel.     

Microstructure and Mechanical Properties of Extruded Magnesium-Aluminum-Cerium Alloy Tubes

Current commercial magnesium extrusion alloys do not offer desirable combinations of strength, ductility, and extrusion speed for automotive structural applications. The effect of small additions of cerium (Ce) to pure magnesium (Mg) and Mg-3 pct Al alloy extruded tubes has been studied. The results suggest that 0.2 pct Ce addition can significantly improve the extrudability and mechanical properties of the Mg extrusions. The improvement in mechanical properties is due to grain refinement and dispersion strengthening provided by the Mg₁₂Ce particles and the beneficial texture obtained. Higher Ce contents further increase strength, but significantly reduce ductility and cause excessive surface oxidation during extrusion. The beneficial effect of 0.2 pct Ce on mechanical properties of pure Mg is not observed when it is added to Mg-3 pct Al alloy, due to the higher affinity of Ce to Al to form the Al₁₁Ce₃ phase in the Mg-Al-Ce ternary alloys. The Mg-0.2 pct Ce alloy is a promising base alloy for further development in automotive applications; however, Al should be avoided in Mg-Ce–based extrusion alloys.     

Microstructural changes in alloy 625 due to creep and characterization using NDE techniques

Alloy 625 exposed to 60,000 hours of service was re- solution annealed at 1433 K and thermally aged at various temperatures in the range of 923–1123 K to produce different microstructures. The microstructures were characterised using scanning electron microscope. Tensile properties and hardness were determined using nondestructive ball indentation technique. Precise ultrasonic velocity measurements were carried out to evaluate the microstructures. A direct correlation has been observed between ultrasonic velocity and mechanical properties. This study demonstrates the feasibility of applying ultrasonic velocity measurements on-line for nondestructive evaluation of mechanical properties of alloy 625.     

Investigations on metallurgical and mechanical properties of CO2 laser beam welded Alloy 825

In the research work, an attempt is made to join nickel-based alloy 825 by employing CO₂ laser beam welding. Successful full penetration weld joint of a 5?mm thick plate is achieved with a very low heat input of 120?J-mm^?1. Narrow weld bead width of 0.6?mm at the root and 1.6?mm at the cap is observed fusion zone; the interface and base metal microstructures have been examined using both optical and scanning electron microscopic techniques to understand the microstructural changes which have occurred due to laser welding. A range of tests of Vickers micro hardness, tensile and impact tests had been performed on the weldment to ascertain the mechanical properties of the joint. Tensile failure at the base metal and a 180° root bend test conducted on the weldment ascertain the soundness of the weld joint produced. An attempt is made to correlate the microstructure and mechanical properties of the weldment. Intermetallics TiN and Al₄C₃ observed in the SEM\EDS analysis at the fusion zone are found to have improved the weld metal strength and hardness.     

Synthesis and properties of ceramics in the SiC — B4C — MeB2 system

The effect of impurities and additives of titanium and zirconium borides on the structure and mechanical properties of SiC — B₄C ceramics over a broad temperature range has been investigated. The ceramics was fabricated by hot pressing without a protective medium. Introduction of borides is accompanied by improvement in all the studied mechanical properties at room temperature, and the nature of hardening of the ceramics is practically independent of the type of SiC powders used. At high temperatures, the mechanical behavior of the ceramics is determined by the impurity composition: the ceramics obtained using abrasive powders loses strength beginning at 600°C, while using powders with decreased impurity content makes it possible to preserve the strength of the material up to a temperature of 1400°C. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 29–42, May–June, 2000.