Needle-like Precipitates Research Articles

Microstructural characterization of the HAZ in AISI 444 ferritic stainless steel welds

Ferritic stainless steel is used as a coating for equipment in the petroleum refining industry. Welding is the main manufacturing and maintenance process used. However, little information on the metallurgical alterations caused by welding of these steels is found in the literature, prompting this study. In this study the authors evaluated the HAZ microstructure of AISI 444 ferritic stainless steel welded plates, by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that a weld thermal cycle caused microphase precipitation in the HAZ of the ferritic stainless steel. Also needle-like Laves phase precipitation occurred in the HAZ, near the partially-melted zone. Other secondary phases such as chi and sigma were observed, as well as nitride, carbide and carbonitride precipitates.

Surface Modification of Titanium with Hydrothermal Treatment at High Pressure

Surface modification of titanium was investigated by means of hydrothermal treatment with a maximum pressure of 6.3 MPa (280 degrees C temperature) in CaO solution or water to improve bioactivity and biocompatibility. As a result, calcium titanate was formed on the titanium surface. Moreover, titanium oxide and titanium hydroxide layers on the surface increased as temperature and pressure increased. The surface-modified titanium was also immersed in a simulated body fluid (SBF) to estimate its bioactivity. Needle-like apatite precipitation was observed on all hydrothermal-treated titanium surfaces after immersion in SBF for four weeks. In particular, the apatite precipitation of titanium treated with 6.3 MPa in CaO solution was clearer and larger in amount than those of all other hydrothermal-treated specimens. Further, the amount of precipitate corresponded to the thickness of the surface-modified layer and the amount of calcium in the surface layer. The results suggested that surface modification of titanium with high-pressure hydrothermal treatment seemed to improve bioactivity and biocompatibility.

TEM characterization of the precipitation reaction in Ti–48Al–10Nb alloy

A detailed transmission electron microscopy (TEM) study has been made of the morphology and the crystallographic characteristics of precipitation of the γ 1-Ti 4Nb 3Al 9 in the γ-TiAl matrix in Ti–Al–Nb system. It is revealed that the γ 1-Ti 4Nb 3Al 9 precipitates, which are formed by a normal quench at 1473 K and ageing treatment at 1073 K, take needle-like morphology with a growing axis parallel to [0 0 1] direction of the matrix. The needle-like precipitates act as barrier grid to inhibit dislocation moving on the slipping plane {1 1 1} of the γ-TiAl matrix, which helps to improve the strength of the alloy. Selected electron microscopy analysis shows that the orientation relationship between the γ 1 phase and the γ-TiAl matrix is [0 0 1] γ1//[0 0 1] γ, (1 0 0) γ1//(1 1 0) γ and ( 0 1 0 ) γ 1 / / ( 1 ¯ 1 0 ) γ . The needle-like morphology of the precipitated phase is discussed with the coherency stress across the precipitate/matrix interface that is considered to be the main factor controlling the precipitate morphology.

Characterisation of nickel based hardfacing deposits on austenitic stainless steel

Nickel based hardfacing alloys Colmonoy-5 and Colmonoy-6 deposited on type 316L austenitic stainless steel substrate using the gas tungsten arc welding process, were characterised for their microstructure and hardness variations across the deposit/substrate interface, and for identification of the principal precipitates present in these hardface deposits. Hardness measurements and electron probe microanalysis (EPMA) across the interface revealed the presence of a dilution zone 2·5 mm wide in the Colmonoy-6 deposit and 1·5 mm wide in the Colmonoy-5 deposit. EPMA and X-ray diffraction studies of the precipitates showed that he blocky type precipitates were chromium borides and the needle-like precipitates were chromium carbides. Also, stress relief heat treatment at 1123 K for 4 h was found to have no significant effect on the hardness of these hard face deposits.

The microstructural evolution of NbAlV ternary alloys

The microstructural evolution during annealing of a series of Nb–Al–V alloys has been studied using electron microscopy. A modified isothermal section of the Nb–Al–V ternary phase diagram is presented. The B2 phase is prominent in the as-cast alloys. On annealing, needle-like A15 particles precipitate in the metastable B2 phase around the grain boundaries. These then spread throughout the grains. The transformation process is very slow when the alloys are annealed below 1273 K due to the difficulty of nucleation. Cold working before annealing can increase effectively the A15 nucleation rate and refine the microstructure.

The effect of tempering on low cycle fatigue behavior of Al-2024

A low cycle fatigue study on Al-2024 polycrystalline alloy was conducted under symmetric tension-compression at room temperature, using a servo-hydraulic testing machine, to investigate the effect of tempering on cyclic deformation. The tests were conducted at constant frequency for O-temper condition and a constant strain rate for T6-temper condition. The fatigue response of the alloy was evaluated macroscopically in terms of cyclic stress strain response and microscopically in terms of appearance of cyclic slip bands. It was found that the cyclic stress strain response of O-tempered alloy exhibited an increase in saturation stress with plastic strain whereas the cyclic stress strain response of T6-tempered alloy exhibited a definite plateau region where the saturation stress remained constant with plastic strain. The T6-temper alloy showed the presence of persistent slip bands (PSBs), which were extending across the grain at 45° orientations from the grain boundary. No (PSBs) were observed in the microstructure of the O-temper alloy; however, precipitate free zone (PFZ) was observed adjacent to the grain boundaries. Needle-like precipitates were also observed within the grains with two different orientations and the angle between them was 65° in the O-tempered alloy.

Transmission electron microscopy investigation of fullerene nanowhiskers and needle-like precipitates formed by using C60 and (η2-C60)Pt(PPh3)2

Nanowhiskers and needle-like precipitates obtained by the liquid-liquid interfacial precipitation method for the systems of isopropyl alcohol and toluene solutions of C60 and (η2-C60)Pt(PPh3)2 were examined by transmission electron microscopy. Morphology of the C60 precipitates was remarkably changed by the addition of (η2-C60)Pt(PPh3)2 in the C60 toluene solution, and capsular needle-like crystals of C60 were formed. C60 cages were found to be directly contacted along the growth axis of (η2-C60)Pt(PPh3)2 needle-like crystals.

Intermetallic compounds in thixoformed aluminium alloy A356

The microstructure of as thixoformed alloy A356 has been investigated by means of optical metallography and transmission electron microscopy. Inhomogeneous deformation of the Al phase during thixoforming was observed and a local cooling rate of 160 K s-1 was estimated. The high cooling rate resulted in the formation of a wide variety of intermetallic phases. Four Fe rich phases, two Mg-Si phases and one phase containing Sr were identified by selected area electron diffraction and energy dispersive X-ray analysis. Fine needle-like precipitates were observed in the Al matrix after a T6 heat treatment.

Synthetic study of Al–Ni alloy system using HVEM and ion accelerator

The microstructure changes of aluminum under implantation with Ni+ ions were investigated. The ion implantation was carried out at 250keV. Needle-like precipitates were formed in the Al matrix after implantation to 0.2×1017Ni+cm−2. This precipitate contained between 8.5 and 13.3at.% Ni. The growth of the precipitates was connected with an amorphous phase under further implantation up to 2×1017Ni+cm−2. The concentration of Ni in the amorphous phase was 10.8–12.8at.%. In order to investigate the phase stability of the precipitate, annealing or electron irradiation experiments were performed in a high voltage electron microscope. The crystalline and the amorphous phases were stable under electron irradiation up to 5dpa. The crystalline phases were also stable during annealing at 673K, whereas the amorphous phase was crystallized during annealing at 593K.

Microstructure in vanadium irradiated by simultaneous multi-ion beam of hydrogen, helium and nickel ions

Pure vanadium was irradiated at 500 and 600 °C by either 5 MeV Ni ions (single beam) or Ni+H and He ions simultaneously. The pure vanadium was of nominal 99.8% purity. For the quantitative investigation of damage structure as a function of the depth, we utilized focused ion beam (FIB) microscopy. To preserve the surface of ion-irradiated metals, we deposited tungsten on the irradiated surface. The specimens were electro-polished to remove the damaged region by FIB. When only nickel ions were used, voids formed in the region from the surface to a depth of ∼0.5 μm when irradiated at 500 and 600 °C. However, in the region of the damage peak, voids were not observed. Needle-like precipitates of about 100 nm of length were observed for any specimen covering the full ion penetration depth. It is thought that the precipitate is a carbide. Moreover, in the specimen irradiated at 600 °C, the granular precipitates were over the region of the 1.0–1.5 μm depth. Void formation was observed over the whole ion penetration depth when the specimen was subjected to Ni+He simultaneous irradiation. Needle-like precipitates were observed.

The effect of plastic deformation on structure and properties of chosen 6000 series aluminium alloys

In order to determine the effect of increased copper addition on the strengthening behaviour during deformation and subsequent ageing, two types of Al alloys were continuously cast and extruded: 6013 containing 1.15% Mg, 1.08% Si, 0.7% Mn, 0.3% Fe and 1.1% Cu, and 6XXX alloy containing 1.09% Mg, 0.9% Si, 0.1% Fe and 1.6%Cu (in wt.%). The 6XXX alloy aged at 165°C showed a hardness maximum of 150 HV, while alloy 6013 revealed lower precipitation hardening at higher strain hardening. A similar maximum hardness of about 170 HV was observed for both alloys after ageing in a deformed state. Transmission electron microscopy performed after deformation of 60% and 90% by cold rolling showed the presence of large, elongated subgrains. Narrow deformation bands consisting of fine subgrains of large misorientation were observed in the alloys deformed 60% by rolling, and their density increased in the alloys deformed up to 90%. Fine precipitates were observed after an ageing time corresponding to the maximum of hardness for alloy 6XXX deformed in the as quenched state. They formed predominantly on dislocations as confirmed by dark field imaging. In the alloys deformed by 60% the precipitates were identified as belonging to the metastable B2 phase. In the alloy deformed by 90%, larger needle-like precipitates were observed. They seemed to possess a quaternary Q-precipitate structure. A frequent rotational moire pattern observed in this state allowed a misorientation as 2–3° to be determined. The presence of fine subgrains formed after ageing indicated the activation of recovery process at the ageing temperature.

Invariant line and crystallography of HCP?BCC precipitation

The method of calculating the invariant line in HCP→BCC precipitation based on the invariant line strain model is described. The experimentally determined crystallographic features of the lath-shaped or needle-like precipitates formed in the HCP→BCC precipitations occurring in Mg−Al and Zr−Nb alloys were found to be in excellent agreement with the predictions from the model, thus suggesting that the model is valid for predicting the crystallography of diffusion-controlled phase transformations.

Precipitation behavior and its effect on strengthening of an HSLA-Nb/Ti steel

The precipitation behavior of a commercial high-strength low-alloy (HSLA) steel microalloyed with 0.086 wt pct Nb and 0.047 wt pct Ti has been investigated using transmission electron microscopy (TEM) and mechanical testing. The emphasis of this study is to compare an industrially hot-rolled steel and samples from a laboratory hot torsion machine simulation. From TEM observations, the Ti and Nb containing precipitates could be grouped according to their size and shape. The precipitates in order of size were found to be cubic TiN particles with sizes in the range of 1 µm, grain boundary precipitates with diameters of approximately 10 nm, and very fine spherical or needle-shaped precipitates with sizes on the order of 1 nm. The needlelike precipitates were found on dislocations in ferrite and constituted the dominant population in terms of density. Thus, they appear to be responsible for the precipitation strengthening observed in this steel. Aging tests were carried out at 650°C to evaluate the precipitate strengthening kinetics in detail. The strengthening mechanisms can be described with a nonlinear superposition of dislocation and precipitation hardening. The mechanical properties of torsion-simulated material and as-coiled industrial material are similar; however, there are some microstructural differences that can be attributed to the somewhat different processing routes in the laboratory as compared to hot strip rolling.

Nucleation and morphology of barium carbonate crystals in a semi-batch crystallizer

A double-jet feed, semi-batch crystallization system was used to explore the nucleation kinetics, growth kinetics and morphology of barium carbonate crystals under a constant pH value. The nucleation rate and the growth rate can be determined successfully by the initial rate method. The results showed that heterogeneous nucleation is dominant in the primary nucleation mechanism, and the effect of specific power input on the nucleation rate is obvious. The results also showed that the pH and initial concentration of the solution play an important role on the morphology of barium carbonate crystals. The crystal forms are floc, candy-like, olivary with end dendrite, olivary-like and needle-like, depending on the operating conditions. At high to moderate concentrations the floc precipitates are the major products in the pH range of 9.0–10.0. At moderate to low concentrations the candy-like and olivary with end dendrite crystals become the major products. At low concentrations and low pH values the crystal forms are olivary-like and needle-like precipitates. However, the results showed that the crystal forms of barium carbonate are concerned with the nucleation rates. On the other hand, the investigations showed that the well-sharp crystal forms follow the surface-integration growth mechanism and the dendrite crystals obey the diffusion growth mechanism.

Microstructural evolution of DS CM186LC during creep and thermal exposure

Thermal exposure tests were carried out at the same temperature and duration as those of creep tests. Growth of γ′ either in the matrix or in the interdendritic regions was observed during high temperature thermal exposure. The growth of γ′ caused an isolated γ island in the γ/γ′ eutectics within which fine HfC particles precipitated. Some directional coarsening of γ′ was found in the specimens exposed at 1050°C. MC carbide reaction with the y matrix was observed in crept and thermally exposed specimens. Needle-like precipitate, a kind of TCP, was found in the specimen crept at 1050°C for 400 hours.

Effects of Cold Rolling on the Aging Kinetics in an Al–Mg–Si Based Commercial Alloy

Effects of cold rolling on the aging kinetics in an Al-Mg-Si alloy have been examined mainly by means of differential scanning calorimetry and transmission electron microscopy. The first exothermic reaction detected at temperatures around 350 K in the cold rolled specimen is probably due to the migration of quenched-in vacancies to the dislocations introduced by cold rolling and the molar heat for this reaction is decreased by cold rolling. The subsequent diffuse exothermic reaction may arise from the segregation of solute atoms to the dislocations, Cottrell's atmospheres being formed. The needlelike precipitates formed in the non-recrystallized matrix of the cold-rolled specimens, and this reaction was displaced to lower temperature side by cold rolling. The molar heat and the activation energy for the needle formation did not vary with reduction, but the activation entropy increased.

Precipitation behavior of (Al,Ag) 3Ti and Ti 3AlC in L1 0-TiAl in Ti-Al-Ag system

A transmission electron microscopy (TEM) investigation has been performed on the morphologies of L1 2-(Al,Ag) 3Ti and Ti 3AlC precipitates in L1 0-ordered TiAl(Ag). During aging at temperatures around 1073 K after quenching from 1273 K, TiAl(Ag) hardens by the precipitation of (Al,Ag) 3Ti and Ti 3AlC. TEM observations revealed that plate-like (Al,Ag) 3Ti precipitates lie on {001} planes of TiAl(Ag) matrix in the short aging period and the habit plane changed from {001} to {hhl} after a long period aging or high-temperature aging and finally to {112} of the matrix lattice. At the same time needle-like precipitates Ti 3AlC, which lie only in one direction parallel to the [001] direction of the TiAl(Ag) matrix, appear after long period aging or high-temperature aging. The anisotropic misfits between TiAl(Ag) matrix and L1 2-(Al,Ag) 3Ti and Ti 3AlC are considered to explain the morphologies of L1 2-(Al,Ag) 3Ti and Ti 3AlC precipitates.

シュウ酸による含Ｓｍ有機相からの晶析逆抽出

Precipitation stripping phenomena of samarium oxalate from samarium-loaded D2EHPA solution were studied with a conventional impeller. The effect of intensified mixing induced by ultrasonic irradiation was also examined. Morhological variation as well as size distribution of precipitated samarium oxalate were observed with processing factors such as pH value, C2H2O4 concentration, samarium concentration and D2EHPA concentration under ultrasonic irradiation. The needle-like precipitate was identified as Sm2(C2O4)3・10H2O by XRD. Its shape was not significantly influenced by C2H2O4 concentration, samarium concentration and D2EHPA concentration. The average size of precipitates was 4μm at a rotational speed of impeller of 800 rpm. It decreased to 2μm at 1, 300 rpm. However, the size reduction effect caused by ultrasonic irradiation was not so evident as abserved in cobalt oxalate precipitation. Plate-like morphology appeared by the addition of HCl to aqueous phase.

Microstructure and mechanical properties of a Mg-4Y-3RE alloy processed by thermo-mechanical treatment

Abstract Thermo-mechanical treatments consisting of hot extrusion at 573 or 673 K and artificial aging at 473 K were carried out on a Mg-4Y-3RE alloy. The material extruded at 573 K, followed by aging for 2 h, showed fine needle-like precipitates and the high density of a dislocation cell. This material exhibited a high strength of 370 MPa at room temperature. The material extruded at 673 K exhibited a very small grain size of 1.5 μm and fine spherical precipitates. This material showed not only a high strength of about 300 MPa from room temperature to 473 K, but also superplastic behavior at a high strain-rate of 4×10−1 s−1 and at 673 K. Furthermore, a good combination of high strength and high ductility at room temperature was attained for the material extruded at 673 K. These qualities can likely be attributed to the very small grain size.

Morphology and microstructure of electrochemically deposited calcium phosphates in a modified simulated body fluid

Calcium phosphates were deposited on a pure titanium plate for various loading times under 1.3 and 12.9 mA/cm 2 in a modified simulated body fluid at 52–92°C. The plate-like crystals formed under 1.3 mA/cm 2 were identified to be octacalcium phosphate (OCP) and/or carbonate-containing apatite. OCP converted to carbonate-containing apatite with the elapsing time of the loading current. The needle-like precipitates formed under 12.9 mA/cm 2 were identified to be carbonate-containing apatite crystals elongated parallel to the c-axis direction. The degrees of crystallinity of the deposits formed under 1.3 mA/cm 2 showed the highest value around 72°C, whereas those under 12.9 mA/cm 2 increased with the electrolyte temperature. The carbonate content of the deposits decreased with the electrolyte temperature and the flow current. The degree of crystallinity of the electrochemically deposited calcium phosphates decreased with the carbonate content.