Formation Of Second Phase Particles Research Articles

Temperature-dependent hardening of zirconium alloys under heavy ion-irradiation: Experimental observation and theoretical analysis

In this work, microstructure observation and thermo-mechanical property characterization of ion-irradiated Zr-0.5Sn-0.5Nb-0.3Fe-0.015Si alloys were addressed by both experimental measurements and theoretical analyses. In experiments, 6 MeV Au3+ irradiation was carried out for Zr alloys with the irradiation dose up to 30 displacements per atoms (dpa). Transmission electron microscopy (TEM) indicated the addition of solute elements could facilitate the formation of second phase particles (SPPs) like (Zr, Nb)2Fe, Zr(Nb, Fe)2 and Zr-Nb-Fe-Si precipitates in the unirradiated matrix, which were then transformed from the crystalline to amorphous state during the irradiation process. Moreover, it was indicated that there existed microband structures with different orientations inside the grains, and the actual irradiation depth had exceeded the value predicted by the SRIM simulation. The influence of irradiation-induced defects on the macroscopic mechanical behaviors of Zr alloys was characterized by both nano-indentation test (NIT) at 298 K and high-temperature nano-indentation test (HTNIT) at 573 K and 673 K. To theoretically address the hardness-indentation depth relations of ion-irradiated Zr alloys at elevated temperatures, a mechanistic model considering the underlying hardening mechanisms was developed. It was revealed that the irradiation hardening behavior was attributed to the contribution of irradiation-induced defects, while the decrease of hardness at elevated temperatures was ascribed to the weakening of all hardening mechanisms. In addition, with increasing indentation depth, the dominant hardening mechanisms changed from the contribution of irradiation-induced defects and geometrically necessary dislocations (GNDs) to those of statistically stored dislocations (SSDs).

High temperature nano-indentation on the mechanical properties of Zr and Zr–Fe alloys: Experimental and theoretical analysis

In this work, the microstructure and subsurface hardness of pure Zr and Zr-xFe (x = 0.2, 0.4, 0.6) model alloys were investigated at elevated temperatures (298–573 K) by means of scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) analysis, transmission electron microscope (TEM) and high temperature nano-indentation test (HTNIT). Corresponding experimental results indicated that the addition of Fe element could lead to grain refinement for Zr–Fe alloys, and facilitate the formation of second phase particles (SPPs) like Zr3Fe precipitates and spherical particles in the matrix, which were in a close relationship with materials hardening. In order to address the hardness-indentation depth relation of Zr–Fe alloys with temperature effect, a mechanistic model was developed that covered the hardening mechanisms of lattice friction, precipitation hardening and dislocation interaction. Related theoretical analysis showed that all the three hardening mechanisms got weakened at high temperatures, which led to the decrease of materials hardness with increasing temperature. Moreover, the noticeable indentation size effect (ISE) was dominated by the formation of geometrically necessary dislocations (GNDs), and increasing temperature could result in the density decrease of GNDs due to the expansion of the plastic zone at elevated temperatures. With the increase of the indentation depth, the dominant hardening mechanism changed from the contribution of GNDs to that of statistically stored dislocations (SSDs). The results obtained in this work can help comprehend the effect of Fe element on both the microstructure and mechanical properties of Zr–Fe alloys at high temperatures.

Effect of Niobium and Titanium Addition on Formation of Second Phase Particles in CHQ Steel Using Transmission Electron Microscope

It is common practice that formation of second phase particles such as nitrides or carbides in the steel matrix has significant role to control the grain size of steel. An attempt is made in the present research work to find out the role of nitrogen to form the nitride particles either with Al, Ti, B, Cr or Si. Two steel samples Steel-A and Steel-B with same titanium and aluminum weight percent in the chemical composition were obtained in hot rolled conditions from international market with only the difference of presence of Niobium in Steel-A. Solution heat treatment was performed at 1350°C with 60 minutes holding time in protherm heat treatment furnace available locally was used to dissolve the particles and then steel samples were reheat treated at 800°C with holding time of 60 minutes and water quenched and microstructure was revealed. Transmission electron microscope connected with Ehlers-Danlos Syndrome (EDS) was used to reveal the morphology of second phase particles. Both samples for a high resolution power Transmission Electron Microscopy (TEM) (Jeol JEM 3010) analysis were prepared by using carbon extraction replica method in 5% Nital solution as an etching technique. Both samples were then caught in copper grid of 3mm for using TEM analysis. TEM micrographs clearly revealed the second phase particles in the matrix of steel. The EDS peaks were studied and it was found that the peaks showed the titanium peaks in both the samples A and B and surprisingly there was no any peak found for aluminum. Stoichiometric calculations were carried out and it was found that weight percent nitrogen required for forming TiN is 0.0073, however the total nitrogen present in both the steels A and B is 0.0058 and 0.0061 respectively. That means that all the nitrogen present in the steel matrix was consumed by titanium to form the Titanium Nitride (TiN) so there was no nitrogen remain to fulfil the requirement of aluminum to form the Aluminum Nitride (AlN) particles.

Si-mediated reassembly of interfacially segregated Sc atoms in an Al–Cu–Sc alloy exposed to high-temperature creep

The formation of second-phase particles by solid-state precipitation is well-known as the most effective strengthening method for the light-weight aluminum (Al) alloys. Here, the interfacial evolutions from Sc solute segregation to Al3Sc precipitation at θ′-Al2Cu/matrix interfaces were investigated in an Al–Cu–Sc alloy crept at beyond 300 °C. By considering the trace Si impurity, it is proposed that Al3Sc precipitation preferentially occurs at the Si-concentrated interfacial locations, i.e. growth ledges. Two effects of interfacial Al3Sc precipitation on θ′-Al2Cu were demonstrated: (1) The Al3Sc precipitation was processed at the expense of the adjacent Sc segregation and allows localized θ′-Al2Cu decomposition, causing “precipitate splitting”. (2) The Al3Sc-enclosed growth ledges resultantly prevented θ′-Al2Cu from coarsening and equilibrium transformation to θ-phase at temperature as high as 400 °C. This work is expected to provide a precipitate-stabilizing strategy by interfacial architecture to maintain the closely spaced dispersion of precipitates and its strengthening contribution at elevated temperature.

Effect of Interlayer Interval Time on the Microstructure and Mechanical Behavior of Additively Manufactured WE43 Mg Alloy

Additive manufacturing of magnesium (Mg) alloys has gained interest for the potential to fabricate complex geometries for extreme light-weighting or improved functionality. In this study, the effect of interlayer interval time and post-deposition processing (i.e., heat treatment and hot isostatic pressing (HIP)) on the microstructure and mechanical behavior of WE43 Mg specimens fabricated by laser powder directed energy deposition (LPDED) was investigated. Microstructure characterization was conducted using optical microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy. Mechanical behavior was evaluated using microhardness and uniaxial tensile testing. Post-processing resulted in improved yield strength, tensile strength, and ductility, which was attributed to a reduction in porosity and, to a lesser extent, the formation of second phase particles. The as-deposited specimens exhibited porosity below 3 pct and HIP treatment reduced porosity to below 0.1 pct. HIP specimens, processed with low interlayer interval time, exhibited the best combination of strength (~ 243 MPa tensile strength) and ductility (~ 9 pct elongation). Changes in interlayer interval time had limited impact on the grain size, hardness, or yield strength. However, increased interlayer interval time (~ 112 pct increase) caused a slight increase in gas porosity and dramatic reduction in tensile strength and ductility, which was attributed to the formation of lack-of-fusion defects in interlayer regions.

Understanding the Effect of Aluminum Addition on the Forming of Second Phase Particles on Grain Growth of Micro-Alloyed Steel

The formation of second phase particles in the steel matrix during melting and casting plays an important role in controlling the grain size of steel. An attempt is made in the present work to find the role of nitrogen on forming nitride particles either with aluminum or titanium. Two steel samples with the same titanium and aluminum weight percent in their chemical composition were collected after the hot rolling process. Solution heat treatment at 1350°C for 60min holding time was used to dissolve the particles and then the steel samples were reheated at 800°C for 60min, water quenched and their microstructure was revealed by usual grinding and polishing process using 2% Nital. A transmission electron microscope connected with EDS was used to reveal the morphology of the second phase particles. The samples for TEM analysis were prepared by the replica extraction method in 5% Nital solution. The samples were then caught in 3mm copper grid for TEM analysis. TEM micrographs revealed the second phase particles in the matrix of steel. EDS peaks were studied and titanium peaks were found in both samples and surprisingly there was not any peak found for aluminum.

Effect of vibration on the formation of second phase particles in cast-rolling strips

Taking 20CrMn steel as the experimental object, the vibration and non-vibration cast-rolling comparison experiments were carried out on the self-developed twin-roll strip vibration cast-rolling mill. And a series of tests such as tensile test, fracture morphology observation and energy spectrum analysis were carried out on the obtained cast-rolling strips. This paper focuses on the analysis of the test results from the perspective of the second phase particles, in order to explore the effect of vibration on the precipitation of the second phase particles in cast-rolling. The analysis results show that the vibration can promote the uniform distribution of alloying elements, thereby inhibiting the formation of large size second phase particles which are mainly concentrated in the central region of the strip in the late solidification stage, and promoting the precipitation of the dispersed small-sized particles in the high-temperature plastic deformation stage, and finally improving the mechanical properties of the cast-rolling strip. At the end of the paper, the influence of vibration parameters such as vibration amplitude and vibration frequency on the formation of second phase particles is further analyzed.

CORROSION CHARACTERISTICS OF AL-0.91MG-0.55SI-1.12FE-0.39CA AL-ALLOY AGED AT ELEVATED TEMPERATURE IN 0.8MH2SO4 SOLUTION

The study of degradation of Al-0.91Mg-0.55Si-1.12Fe-0.39Ca aluminum-alloy is carried out under different state of microstructure. The reason for this work is to decide the impact of heat treatment on the microstructure and the corrosive consumption of Al-alloy in acid utilizing weight reduction system. Specimens were solution treated at 545 o C and artificially aged at 185 o C. The maximum hardness is found after aging for 12 hrs. They were immersed in 0.8 molar solution of sulfuric acid for 0.58 hrs, 1.08 hrs, 1.58, 2.08 hrs and 2.58 hrs. The corrosion rates were calculated for various immersion periods. The test work has uncovered that time and temperature assumes an imperative part in the precipitation transformation procedure of the Al-ally. The hardness increases due to formation of second phase particles of Mg2Si. In over-aging of the alloy, the growth of the precipitate particle takes place at the expense of smaller precipitate particles. The rate of corrosion is found lower in the artificially aged specimen. The corrosion rates are found stabilized after 2.08 hrs of immersion in H2SO4. The X-Ray Diffraction patterns are also analyzed in the range of 10-80⁰ which are showing peaks of aluminum solid solution and Mg2Si in the different patterns.

FeAl Based Intermetallic Matrix Composites Through Melt Route

FeAl based composites reinforced by carbide particles have attracted much attention in the recent years. In the present study, FeAl based composites were prepared by using arc melting route in argon atmosphere. The Ti/Zr addition to FeAl based alloys containing carbon have produced in situ formation of second phase particles namely TiC/ZrC respectively. The in situ precipitated TiC/ZrC carbides were found to be thermally stable and improved the mechanical properties of FeAl. The influence of these alloy carbides on the mechanical properties of FeAl based composites were studied. The addition of Ti/Zr resulted superior strength than FeAl alloy containing carbon. The mean coefficient of thermal expansion (CTEs) of FeAl based composites were also measured. The presence of these carbides significantly affected the CTE of FeAl based composites.

Effect of minor carbon additions on the high-temperature creep behavior of a single-crystal nickel-based superalloy

Different amounts of carbon were added to a single-crystal nickel-based superalloy. The microstructural evolution of these alloys before and after high-temperature creep tests was investigated by employing scanning electron microscopy and transmission electron microscopy. Upon increasing the carbon contents, the volume fraction and diameter of the carbides increased gradually: however, the creep lives of the alloys increased slightly at first and subsequently decreased. The formation of second-phase particles, such as the nano-sized M23C6, blocky and needle-shaped μ phase, was observed in the creep samples, which was closely related to the high-temperature creep behaviors.

The Role of Metallurgical Solid State Phase Transformations on the Formation of Residual Stress in Laser Cladding and Heating<sup></sup>

There are two major types of solid state phase transformations in metallic materials; the formation of second phase particles during heat treatments, and the transformation of the matrix from one crystalline packing arrangement to another during either heating or cooling. These transformations change the spacing between adjacent atoms and can thus influence the residual stress levels formed. The heating and cooling cycles of materials processing operations using lasers such as cladding and melting/heating, can induce phase transformations depending on the character of the material being processed. This paper compares the effects of the different phase transformations and also the influence of the type of laser processing on the final residual stress formed. The comparisons are made between laser clad AA7075, laser clad Ti-6Al-4V and laser melted nickel-aluminium bronze using neutron diffraction and the contour method of measuring residual stress.

Behavior and effect of Ti2Ni phase during processing of NiTi shape memory alloy wire from cast ingot

Binary NiTi alloy is one of the commercially successful shape memory alloys (SMAs). Generally, the NiTi alloy composition used for thermal actuator application is slightly Ti-rich. In the present study, vacuum arc melted alloy of 50.2Ti–Ni (at.%) composition was prepared and characterized using optical, scanning and transmission electron microcopy. Formation of second phase particles (SPPs) in the cast alloy and their influence on development of microstructure during processing of the alloy into wire form has been investigated. Results showed that the present alloy contained Ti2Ni type SPPs in the matrix. In the cast alloy, the Ti2Ni particles form in varying sizes (1–10μm) and shapes. During subsequent thermo-mechanical processing, these SPPs get sheared/fragmented into smaller particles with low aspect ratio. The presence of SPPs plays a significant role in refinement of the microstructure during processing of the alloy. During deformation of the alloy, the matrix phase around the SPPs experiences conditions similar to that observed in severe plastic deformation of metallic materials, leading to localized amorphisation of the matrix phase.

Microstructure and mechanical properties of hot rolled Fe–40 at-%Al intermetallic alloys with Zr and B addition

The microstructure and mechanical properties of hot rolled Fe–40 at-%Al based intermetallic alloys, with 0·1 at-%Zr and different additions of B (varying from 0·01 to 0·1 at-%), are characterised. The additions of Zr and B improve tensile properties at room and elevated temperatures. Increasing B content is also associated with a number of other effects. First, the fracture mode changes from intergranular decohesion to cleavage, which correlates with significant increases in the fracture toughness. Second, there is a certain stabilisation of dislocations arranged in parallel systems of slip bands, as shown by transmission electron microscopy. Numerous complex stacking faults on {100} planes are also observed in the alloy with the highest B content. Third, B is found to modify the formation of second phase particles; such particles (coarse and fine) are analysed by energy dispersive X-ray spectroscopy and electron energy loss spectrometry to obtain compositional information.

Mechanism of creep deformation of Alloy 230 based on microstructural analyses

Creep testing of Alloy 230 was performed at 750, 850 and 950 °C under applied stresses equivalent to its 10% and 25% yield strength (YS) values. The results indicate that this alloy satisfied the maximum allowable creep strain of 1% when loaded to 0.10YS level at these temperatures. Microscopic evaluations revealed the formation of second phase particles including superstructures and carbide precipitates as a function of temperature. The enhanced plastic strain at 0.25YS stress level at 950 °C was attributed to dislocation glide, subgrain formation, and recrystallization.

Grain size dependent tensile behavior of Mg–3%Al alloy at elevated temperatures

In this study, we experimentally investigate the effect of grain size on the tensile properties of Mg–3%Al alloys at elevated temperatures. Bulk nanostructured Mg–3%Al alloys were prepared by mechanical alloying followed by conventional sintering and extrusion. The microstructure and grain size were investigated by XRD, field emission scanning electron microscope (FESEM) and optical microscope. The formation of second phase particles was observed in nanostructured powder and the extruded bulk samples. Tensile tests were performed at elevated temperatures up to 250 °C and the yield strength, tensile strength and elongation to failure were measured for microcrystalline and nanocrystalline samples. Remarkably, the strain to failure was observed to be non-monotonic with temperature with the failure strain increasing up to a critical temperature and decreasing thereafter. This critical temperature was found to be strongly dependent on grain size. This phenomenon is attributed to a competition between uniform elongation and necking deformation. The latter dominates at higher temperatures due to decreased strain hardening, particularly in the fine grained samples.

Enhancement in fracture toughness of PZT ceramics by in-situ precipitation of CeO2

Samples of lead zirconate titanate (PZT) with part of Zr in the composition corresponding to the morphotropic phase boundary (MPB) replaced with different amounts of Ce have been prepared according to the formula Pb(Zr0.535-δTi0.465Ceδ)O3 with δ between 0.0 and 0.05. The sintering has been carried out without any atmosphere powder so as to provide a Pb deficient atmosphere and facilitate the formation of second phase particles. The loss of weight during sintering increases sharply with the initial addition of CeO2 upto δ = 0.0025. The sintered density decreases with the initial addition of CeO2 and then increases, reaching a maximum value at δ = 0.006. The x-ray and weight loss data point to Ce going to the A site in samples with low CeO2. Particles of a CeO2 rich phase are found to form for δ > 0.02. Presence of the second phase particles leads to a significant enhancement in the fracture toughness, KIC, of samples with CeO2 ≥ 0.02. The strength decreases with increasing CeO2 addition and increasing sintering time. These two factors also lead to increased PbO loss during sintering. Highest values of KIC (∼2.9 MPa ml/2) are found in samples with δ= 0.05, sintered for 2 h.

Dispersoid additions and their effect on high temperature deformation of FeAl

Small additions of carbon and ZrB 2 have been introduced into an FeAl alloy in order to obtain homogeneous distributions of different dispersoid particles in the B2 matrix. The carbon additions have produced the formation of second phase particles with a complex cubic structure (perovskite). The influence of these particles on the room and high temperature yield strength of the intermetallic has been compared to that of the ZrB 2 particles. Tensile tests of these alloys have been performed between 25°C both types of particles produced a substantial increase, only the ZrB 2 particles retain much of this strength at 600°C. The much faster decrease of stregth with temperature observed in the carbon containing alloy is explained in terms of a deformation process where the perovskite particles constitute a composites material with the matrix deforming at different rates.

The study of second phase particles in grain oriented 3%Si-Fe

The compositions of the second phase particles in grain oriented 3%Si-Fe have been studied by using the scanning transmission electron microscope (STEM). Second phase particles have been extracted from hot rolled band, primary recrystallized samples, and samples at the early stage of secondary recrystallization. The results of x-ray microanalysis have indicated that copper is a key element in the formation of second phase particles in both conventional and high permeability grain oriented 3%Si-Fe, and thus plays an important role in primary grain growth inhibition. The changes in the composition of the particles through the processes have also been studied.

Formation of second phase particles in aluminum-copper alloy films

The formation of second phase particles in Al+3% Cu alloy films was examined in order to find differences of the precipitation in thin films from that occurring in bulk alloys. Compared to bulk alloys in the thin film material the formation of Guinier-Preston zones is retarded. In well quenched thin films 60 h at 100°C or 6 h at 130°C are necessary to produce G.P. zones. θ′ particles are nucleated after approximately 100 h at 120°C without formation of θ″. The stable θ-Al 2Cu precipitate was found at temperatures as low as 150°C on the film surface. The results show that excess vacancies cannot be retained in thin films and that the film surfaces provide preferential nucleation sites for the equilibrium precipitate θ-CuAl 2.