Influence Of Microstructural Changes Research Articles

Influence of Gama Prime Changes on the Heat Transport Phenomena of a Nickel Super Alloy

The paper deals with the influence of microstructural changes of the nickel superalloy (NiS) on heat transport changes in MAR-M247. The dissolving annealing within the temperature interval of 900 – 1240°C and cooling in water has been applied to enhance structural changes. It has been shown that the narrow connection between the γ’ phase morphology changes, as well as values of density, thermal conductivity and specific heat capacity. In the dissolving annealing process, the γ’ particles change in certain cycles from fine to rough and back to fine one. Obtained results of changes of thermal conductivity, density and specific heat capacity correlate with image analysis and electron microscopy observation.

Investigation on crashworthiness of ultrafine grained A356 sheets and validation of Hall-Petch relationship at high strain-rate deformation

High crushing force and good energy absorption are the essential requirements for structural materials subjected to dynamic loading. In the present work, commercial A356 material is subjected to cryorolling and post-cryoroll annealing to produce sheets of different grain sizes and the influence of microstructural change on dynamic behavior of the material is studied. Dynamic tests are done in a crossbow test equipment at an average strain rate of 250s−1. Quasi-static tests are done at an initial strain rate of 0.005s−1 to compare the dynamic performance of the material with its static/quasi-static behavior. It is found that strength and ductility of cryorolled material at dynamic loading condition is lesser than that in quasi-static loading. Upon annealing, the material performance of the material is found to be better at high strain-rate deformation than that at quasi-static condition. A detailed analysis on the deformation behavior and fracture mechanism of the material at high strain-rate is carried out. Further, the existence of Hall-Petch relationship at high strain-rate deformation is evaluated. The material's strengthening factor is found to hold good agreement to the Hall-Petch relationship with a grain boundary strengthening coefficient of 112MPa at dynamic loading.

Effect of microstructural evolution by isothermal aging on the mechanical properties of 9Cr-1WVTa reduced activation ferritic/martensitic steels

The influence of microstructural changes caused by aging condition on tensile and Charpy impact properties was investigated for reduced activation ferritic-martensitic (RAFM) 9Cr-1WVTa steels having single martensite and a mixed microstructure of martensite and ferrite. For the mixed microstructure of martensite and ferrite, the Charpy impact properties deteriorated in both as-normalized and tempered conditions due to the ferrite and the accompanying M23C6 carbides at the ferrite grain boundaries which act as path and initiation sites for cleavage cracks, respectively. However, aging at 550 °C for 20–100 h recovered gradually the Charpy impact toughness without any distinct drop in strength, as a result of the spheroidization of the coarse M23C6 carbides at the ferrite grain boundaries, which makes crack initiation more difficult.

Effect of grain size and residual stress on the corrosion resistance of friction stir spot welded AZ31B joints

Localized corrosion at the weld periphery of AZ31B friction stir spot welds has been associated with the formation of a galvanic cell between the stir zone material and the adjacent base metal. However, this explanation did not take into account the effects of residual stress and grain growth in material adjacent to the stir zone region. In this study, the influence of microstructural changes on the electrochemical characteristics of FSSW joints is investigated using a combination of microcapillary polarization, stress relief heat‐treatment and micro‐hardness testing. It is confirmed that residual stress has no significant effect on the corrosion resistance properties of completed joints. Also, based on a detailed examination of the electrochemical characteristics of materials in the stir zone, TMAZ and HAZ regions, grain growth had negligible influence on the corrosion resistance properties.

Influence of microstructural changes on the macro response of functionally graded material structures

Macro structural properties of functionally graded material depend on micro net structures. Thus, there is important theoretical significance in studying the influence of material microstructural changes on the macro responses of functionally graded material structures. Here, a new microelement method is proposed. Scale-span analyses between macro responses and micro-constitution were conducted based on metallography input instead of traditional mechanical input of materials parameters. To reflect the actual microstructural changes in functionally graded materials, the microelement method established dense microelements in the normal finite element of the structure, and translated the freedom degrees of all microelemental nodes to the freedom degrees of the same normal finite elements by compatibility conditions. Three-dimensional mechanical analyses of functionally graded material plates with medium components and micro net structures were determined by the microelement method, and the influence of the microstructural changes on macro response distributions was analysed.

Influence of Microstructural Changes in Creep Resistant Steel after Long-Term Creep Tests on the Shape of the Polarization Curves

Creep resistance of the steel depends on chemical and structural composition and structural stability. Therefore it is necessary to check microstructural changes in material during the long-term service, however the necessary material analyses are generally destructive. The submitted contribution describes non-destructive electrochemical method for detection of some microstructural changes taking place during creep exposures. The shape of polarization curves are correlated to the microstructure of CB2 steel, the most promissing (9-12) %Cr martensitic steel for the cast components. The dynamic polarization curves were measured using samples in as received conditions and after long-term creep tests at 650°C. Microstructure was analysed using light and electron microscopy. The microstructure of the CB2 steel changed during creep exposures. In polarization curves additional peak appeared in the main passivation region and the curve shape changed also in the secondary passivation region. The curve changed in dependence on precipitation and growth of Laves phase particles.

Influence of microstructural changes on magnetic refrigeration performance for La(Fe0.94Co0.06)11.8Si1.2 alloys during magnetic field cycling

NaZn13-type La(Fe0.94Co0.06)11.8Si1.2 alloys were manufactured to investigate the influence of their microstructural change on magnetic refrigeration performance during magnetic field cycling. The magnetic refrigeration performance measurements indicate that both the large magnetic entropy change value (ΔS = 14.1 J kg−1 K−1) and maximum adiabatic temperature change (ΔT = 2.2 K) are favorable for the alloys to be superior candidate of magnetic refrigerants. However, the alloys exhibit nearly 10% decrease of ΔS and ΔT when they performed cycling ten-thousand times. More than thousand times of cycles induce local stress and grain cleavages presented by the accumulation of irreversible microstructure changes such as micro-cracks and sub-boundaries. According to the domain observation for the alloys with different field cycles, these microstructure characteristics accompany with the reconfiguration of the local magnetic domains and increase of domain wall energy, which are considered to be the reason of the decrease of ΔS.

Magnetron Sputtering a New Fabrication Method of Iron Based Biodegradable Implant Materials

It was shown in the previous decade that pure-iron has a large potential as a biodegradable medical implant material. It is necessary to tailor the material properties according to the intended use of the device. It is of great interest to investigate not only the influence of processing on the material properties but also alternative fabrication methods. In this work for the first time magnetron sputtering in combination with UV lithography was used to fabricate free standing, patterned pure-iron thick films. For the intended use as biodegradable implant material free standing thick films were characterized in terms of microstructure, degradation performance, and mechanical properties before and after various heat treatments. The influence of microstructural changes on the degradation behavior was determined by linear polarization measurements. The mechanical properties were characterized by tensile tests. Microstructure, surface, and composition were investigated by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) measurements. The foils exhibited a preferential orientation in110direction and a fine grained structure. Furthermore they showed a higher strength compared to cast iron and corrosion rates in the range of 0.1 mm/year. Their mechanical properties were tuned by grain coarsening resulting in a slight increase of the degradation rate.

On the estimation of the magnetic easy axis in pipeline steels using magnetic Barkhausen noise

A method for determination of the magnetic easy axis of the Roll Magnetic Anisotropy in API-5L steels is proposed. The method is based on the fact that the angular dependence of the energy corresponding to the main peak of the Magnetic Barkhausen signal presents uniaxial anisotropy with its easy axis parallel to the rolling direction, independently of the angular dependence of the magnetocrystalline energy in the materials. The proposal is also justified based on the analysis of the influence of microstructural changes, produced by hot-rolling on the domain wall dynamics.

Corrosion behaviour of heavily deformed pearlitic and brass-coated pearlitic steels in sodium chloride solutions

The influence of plastic deformation and galvanic coupling on the microstructure and corrosion behaviour of pearlitic steel and brass-coated pearlitic steel was investigated in sodium chloride solution at 25°C. Microstructural changes were quantified using scanning electron microscopy coupled with EBSD. Chemical and electrochemical modifications were evaluated using XPS, ZRA, the electrochemical microcell technique and the weight loss method. From these experiments, the influence of microstructural changes on the electrochemical parameters and the corrosion rate was discussed.

Influence of Microstructural Changes on Some Macro Physical Properties of Cement Mortar during Accelerated Carbonation

The objective of this work was to examine the changes in the microstructure and macro physical properties caused by the carbonation of normalised CEM II mortar. Samples were prepared and subjected to accelerated carbonation at 20&#176C, 65% relative humidity and 20% CO2 concentration. On the microstructure scale, the evolutions of the cumulative pore volume, pore size distribution, and specific surface area during carbonation were calculated from the adsorption desorption isotherms of nitrogen. We also examined the evolution of macro physical properties such as the solid phase volume using helium pycnometry, porosity accessible to water, gas permeability, and thermal conductivity. The conflict between nitrogen porosity and water porosity results indicated that the porous domains explored using these two techniques are different and help to complementarily evaluate the effects of carbonation. This is a multi-scale study where results on microstructural changes can help to explain the evolution of macro physical properties.

Small punch creep behavior and nondestructive evaluation of long term aged AISI 316L stainless steel

In this work, we have studied the influence of microstructural changes of precipitates such as intermetallic sigma (o) phase and M23C6 carbides on the creep behavior of the high temperature aged AISI 316L stainless steel by nondestructive small punch test and ultrasonic test. Small punch (SP) creep tests were also performed to determine the creep rupture life of these artificially aged specimens. The results of ultrasonic tests characterizing the microstructural changes were compared with those of SP creep tests to produce the equations capable of predicting the creep life by nondestructive method. It was remarkably observed that as the aging time increased, the creep rupture life decreased in response to the coarsening behavior of precipitates.

Annealing Effects on the Microstructure and Mechanical Properties of Cu-Nb Microcomposites

The annealing effects on the microstructure of Cu-Nb microcomposites fabricated by bundling and drawing process have been studied. During annealing at temperature as high as 800, the intensity of (110) diffraction peak of Nb became sharper and higher. The significant cylinderization and coarsening phenomenons of the niobium filaments were observed. The influence of microstructural changes on the hardness and the tensile strengths of Cu-Nb wires were discussed.

Influence of Microstructural Changes on Some Macro Physical Properties of Cement Mortar during Accelerated Carbonation

Influence of Microstructural Changes on Some Macro Physical Properties of Cement Mortar during Accelerated Carbonation

Influence of Microstructural Changes on Impact Toughness of Weldment and Base Metal of Duplex Stainless Steel AISI 2205 for Low Temperature Applications

Austenite (γ) reformation and microstructural changes are the major anxieties in duplex stainless steel welding and aging process. Insufficient stabilization of austenite phases and intermetallic formations due to unfavourable thermal cycle leads to drastic reduction in the ductility and toughness of duplex stainless steel in particularly at low temperature. In this work, an attempt has been made to analyze the microstructure in the DSS weld, heat affected zone and base metal with respect to their impact toughness. DSS weld joints were fabricated using gas tungsten arc welding process with controlled welding parameters. Ferrite austenite ratio in the weld zone, heat affected zone and base metal was assessed by quantitative metallographic image analysis. The impact test results were correlated with the fractured surface and the microstructure of the tested specimens. The effect of heat treatment on the microstructural changes in the weld and base metal were also investigated with respect to impact toughness. Austenite phases were nucleated in the high temperature heat affected zone during heat treatment of weldment at 1050°C for 1 hour and it leads to enhancement in the impact toughness of the DSS weldment. But, drastic reduction in the impact toughness was observed in the base metal after heat treatment at 850°C and 1050°C due to the formation of sigma phase at 850°C and the coarser ferrite and austenite grains and partially dissolved sigma phase in the microstructure of 1050°C heat treated samples.

Effect of sigma phase on near-threshold fatigue crack growth behavior and ultrasonic evaluation in AISI 316L stainless steel

In this work, we examined the influence of microstructural changes, such as an intermetallic sigma (σ) phase, on the fatigue behavior of high-temperature aged AISI 316L stainless steel. Nondestructive ultrasonic test and fatigue crack growth tests were performed to determine the threshold stress intensity factor of these artificially aged specimens. Ultrasonic test results characterizing the microstructural changes were compared with those of the fatigue tests to propose an empirical formula capable of predicting the threshold stress intensity factor by a nondestructive method. We observed a strong correlation between the increase in the volume fraction of the σ phase and the decrease of ΔKth. Ultrasonic velocity increased in response to the coarsening behavior of the σ phase in the vicinity of the grain boundaries.

Effect of microstructure on non-linear behavior of ultrasound during low cycle fatigue of pearlitic steels

Influence of microstructural changes on the second harmonics of sinusoidal ultrasonic wave during low cycle fatigue (LCF) deformation in pearlitic steel was studied. Fatigue tests were interrupted and at every interruption, non-linear ultrasonic (NLU) parameter (β) was determined. Microstructures of cyclically deformed specimens at various cycles were examined by transmission electron microscopy (TEM). The variation of β with fatigue cycles was correlated with the microstructural changes and the results were explained through the variation in dislocation morphology and carbon content of the steel.

Influence of minimum temperature on the thermomechanical fatigue of a directionally-solidified Ni-base superalloy

It is well understood that thermomechanical fatigue (TMF) lives are significantly influenced by the maximum temperature of the cycle since increasing temperature accelerates both creep and the coupled fatigue-oxidation effects, usually exponentially with increasing temperature. Hence, most TMF experiments focus on the impact of the maximum temperature of the cycle along with the phasing of the temperature and strain. Very little focus has been placed on the role of the minimum temperature of the TMF cycle. Usually the minimum temperature is chosen for experimental expediency and is not based on minimum temperature experienced in actual components. For example, in a gas turbine, the minimum temperature for an extended shutdown is near room temperature. This paper shows that out-of-phase TMF with lower minimum temperature while maintaining the same mechanical strain results in lower life. Possible explanations for the reduction in life include the increase in inelastic strain range due to the increase in elastic modulus at lower temperatures and microstructural changes that occur at elevated temperature, reducing the lower temperature yield strength. Both experiments and simulations using crystal viscoplasticity modeling show that the increase in elastic modulus with decreasing temperature leads to greater inelastic strain range and a commensurate reduction in fatigue life. This effect is just as important to consider as the influence of microstructure changes occurring at the elevated temperatures of the cycle.

Corrosion behaviour of aluminium syntactic functionally graded composites

Syntactic Functionally Graded Metal Matrix Composites (SFGMMC) are a type of composites reinforced by microballoons exhibiting a graded reinforcement distribution. These materials constitute a promising new generation of lightweight structural materials for aerospace, marine and shielding/insulation applications. In this work, A356 alloy reinforced with silica-alumina microballoons (SiO2-Al2O3) was processed by casting techniques. The influence of the microballoon distribution gradient on the corrosion behaviour of the composite was investigated by potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS). Composite surfaces were analysed before and after testing by Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) to determine the influence of microstructural changes.

Influence of microstructure changes on corrosion resistance of super duplex stainless steel

Effect of microstructure on pitting corrosion of super duplex was investigated in 3.5% NaCl solution at 90°C. The microstructures were controlled by applying two different cooling rates of water quench and air from the heat treatment temperatures of 1,000°C and 1,300°C. The amount of ferrite and austenite and other precipitates were measured using optical and image analyser. The results revealed that the ferrite percentage increased as the heating temperature increased to 1300°C. Metallographic results showed the presence of intermetallic phases. Back scattering analysis revealed presence of sigma (σ) and chi (χ) phase. The volume fraction of ferrite to austenite as well as the precipitation of harmful intermetallic phase during cooling process affected the corrosion resistance. Reformation of austenite during slow cooling from 1,300°C enhanced corrosion resistance while intermetallic precipitates promoted pitting damage and decreased pitting potential to more active values.