As-produced Condition Research Articles

Effect of thermo-mechanical treatment on cryogenic mechanical properties of a medium-entropy Fe65Co12.5Ni12.5Cr9.5C0.5 alloy produced by the laser-based powder bed fusion

Microstructure and mechanical properties of the Fe65Co12.5Ni12.5Cr9.5C0.5 (in at.%) medium-entropy alloy obtained by the laser-based powder bed fusion (PBF-LB) was investigated in the as-produced condition and after (i) annealing in the interval 800–1100 °C or (ii) cold rolling followed by annealing at 800 °C. The as-produced microstructure was found to be surprisingly stable; noticeable recrystallization occurred only after annealing at 1100 °C. Cold rolling resulted in the formation of typical deformed microstructure, while further annealing led to the formation of a fine-grained recrystallized microstructure. A considerable improvement in cryogenic mechanical properties was obtained after some thermo-mechanical treatments due to the transformation-induced plasticity (TRIP) effect. The cold-rolled alloy had the best cryogenic strength characteristics; yield strength and ultimate tensile strength were found to be 1740 MPa and 2235 MPa, respectively. High strength was combined with a pronounced value of elongation to fracture of 24 %. Detailed analysis of microstructure and corresponding mechanical behavior changes caused by various processing of the as-produced alloy are presented.

Characterization on microstructure of interface and failure analysis of SiC fiber reinforced Ti-17 composites under tension load

In this study, the ultimate tensile strength of unidirectional SiC-fiber/Ti-17 composites was measured in the as-produced condition at room temperature. Fracture and interfacial reaction zone was characterized by using laser confocal microscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy. Elemental distribution maps of the interfacial reaction layer and titanium matrix were quantitatively examined by electron probe micro-analyzer (EPMA). Micromechanical properties of SiC fiber and titanium matrix was inspected by Nano-indentation. The Fracture failure mechanisms was show that the key microstructural parameters which dominate damage initiation, damage growth and fracture behavior of the composites were explained in detail.

Microstructure characterisation and mechanical properties of ODS Eurofer steel subject to designed heat treatments

The present work deals with oxide dispersion strengthened (ODS) Eurofer steel fabricated by powder metallurgy involving mechanical alloying and spark plasma sintering. A heat treatment route including normalising and tempering was applied to the as-produced steel, based on differential scanning calorimetry (DSC) measurement. The microstructure was characterised by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), electrolytic extraction, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermodynamic calculations conducted using Thermo-Calc software were used to determine the precipitation conditions. The results show that the Vickers microhardness of the sample after the designed heat treatment is more uniform compared to the as-produced condition. A dual phase and bimodal microstructure is formed in the as-produced and tempered steels. M23C6 and M6C carbides were found in the as-produced sample while only M23C6 carbides were observed in the tempered sample. The carbides dissolve and reprecipitate during the heat treatment, preferably at the grain boundaries. Nanosized Y2O3 particles were found to be homogenously distributed in the steel matrix, which is crucial for the mechanical properties. The dislocation density in the material is decreased significantly after the normalising and tempering treatment. A yield strength model was developed that includes the strengthening contributions of solid solutes, grain size, dislocation density and nanoparticles. Good agreement is obtained between the experimentally measured and theoretically calculated strength of the as-produced and tempered steels.

Evaluation of the impact behaviour of AlSi10Mg alloy produced using laser additive manufacturing

In the present study, instrumented impact strength tests were carried out on Charpy AlSi10Mg samples produced using laser additive manufacturing in order to accurately investigate the influence of building directions, heat treatment parameters and also the effect of Hot Isostatic Pressing (HIP) on their impact properties. AlSi10Mg cast samples were also tested for comparison. In addition to metallographic inspections, a deep characterization of the fracture surfaces in all the analysed conditions was performed. Microstructural features were also correlated to the impact properties: absorbed energy, peak force, crack nucleation and propagation energies. It was found that additive manufactured samples in as-produced condition exhibit the best performance due to their peculiar microstructure. HIP, followed by T6 heat treatment, is positive for the alloy properties since it effectively reduces porosities, which are a favourable path for crack propagation. Building direction has a clear effect on the fracture propagation. Samples in as-produced condition display greater unevenness of the fracture surface in the horizontal direction than in the vertical direction. This trend is less evident after heat treatment, but still detectable. The fractal dimension of the fracture surfaces is a quantitative parameter sensitive to the building orientation of samples and to the performed heat treatments.

Study of heat treatment parameters for additively manufactured AlSi10Mg in comparison with corresponding cast alloy

A solution, quenching and ageing heat treatment is often performed on additive manufactured AlSi10Mg parts to dissolve the anisotropy due to the layer-by-layer building.This study investigates the influence of temperature and duration of solution and ageing treatment on microstructure, hardness and density of AlSi10Mg alloy produced by direct metal laser sintering.A parallel investigation is carried out on AlSi10Mg samples produced by gravity casting to analyse the different response to the same heat treatment conditions.The highest hardness, combined with an acceptable increase of porosity, is reached after selected heat treatment parameters. It was also found that, compared to the as-produced condition, this treatment leads to a decrease of ultimate tensile strength, without affecting the yield strength of additive manufactured samples, and reduces the difference in properties along the two building directions. The high properties of the as-produced samples are related to the finer microstructure and, as proved by the differential scanning calorimetric measurements, to the self-quenching phenomenon.

In-situ studies on martensitic transformation and high-temperature shape memory in small volume zirconia

Recently, the shape memory effect with significant recoverable shape deformation has been discovered in small volume single-crystal zirconia. The application potential for such shape memory ceramics has spurred in-depth exploration of the martensitic transformation crystallography and high temperature shape memory effect. In this work, the martensitic transformation of micron-sized zirconia has been studied in both a pristine as-produced condition and after micromechanical compression, using synchrotron scanning micro X-ray diffraction (μXRD). The pristine zirconia was found to transform into the monoclinic phase via a different crystallographic path than the compressed zirconia, resulting in distinct monoclinic variant preferences. The characteristic martensitic transformation temperatures were also found to be higher after uniaxial compression than in the pristine condition. Such observations provide insight on the differences between stress-induced and thermally-induced martensitic transformation. Moreover, we have observed a full cycle of the shape memory effect with large recoverable strain (7%) in micron-sized zirconia at a temperature of 400 °C. Our findings provide an important guideline to tailor the high-temperature shape memory properties of zirconia for further scientific research and engineering applications.

Microstructural and Mechanical Characterization of Artificially-Aged Power Plant Steel

Degradation of properties due to ageing at high temperature service is a common problem which normally occurs in electricity generation power plants, refineries, petrochemical industries. This work investigates the influence of accelerated artificial ageing on the microstructural and mechanical properties of 9-12%Cr steel usually used in power plants. This steel was tested in the as-produced and aged for 2, 5 and 8 weeks at 700°C. Results showed that the microstructural features such as phases, carbides, i.e. morphology and type, sub-grains and their boundaries and misorientation angles are the dominant factors influencing the mechanical properties. Ageing led carbides to go into solution in the martensite-ferrite structure and also led to the increase of average misorientation angle as well as to the reduction of low angle grain boundaries. In addition, ageing led to the reduction in the mechanical properties and hardness when compared to the as-produced condition.

Experimental and Numerical Study of Shot Peened Thin Hard-Coated Components

A test bench was designed and assembled to carry out impact tests on samples and components. The system allows simple and rapid adjustment of the test parameters, such as the shot size and air pressure, with good repeatability of the results. Tests on steel and light alloys were carried out under both as-produced condition and on thin hard-coated samples. Significant reductions in dimple dimensions were seen after coating. FE models simulating the experiments overestimated the dimple depths, although the parameter trend was satisfactorily captured. The residual stresses from coating and shot peening determined numerically are believed to have been proven effective against fatigue.

Untersuchung der Mikrostruktur asbesthaltiger Bremsbeläge und Möglichkeiten der Asbestsubstitution / The Microstructure of Brake Lining Materials Containing Asbestos and Possible Asbestos Substitutes

Asbestos-based brake linings from two Iranian manufacturers were investigated using laser scanning and electron microscopy. The composition specified by the manufacturers was confirmed and the arrangement of the various components both before and after braking tests documented. It was shown that the steel swarf particles form primary contact points onto which layers of wear particles adhere. In the as-produced condition and after grinding, numerous fibres of asbestos were observed. After braking trials however only relatively innocuous broken fibre particles were found on the surface of the lining material.

Determination of crack arrest toughness for Russian light water reactor pressure vessel materials

The experimental results of crack arrest fracture toughness for 15X2MFA and 15X2NMFA steels and their welds, produced by submerged arc welding (SAW) are presented. The data base containing 176 test results has been obtained for materials used in the manufacture of the VVER-440 and VVER-1000 reactor pressure vessels in the as-produced condition (BOL) and after embrittlement simulated by heat treatment, corresponding to the material state at the end of life (EOL).

Mechanical properties of vapor-grown carbon fiber composites with thermoplastic matrices

This article discusses the mechanical properties of vapor-grown carbon fiber (VGCF)/nylon and VGCF/polypropylene composites. Fibers in the as-produced condition yielded composites with marginally improved mechanical properties. Microscopic examination of these composites clearly showed regions of uninfiltrated fibers, which could account for the unsatisfactory mechanical properties. The infiltration of the fibers by both polymers was improved by carefully ball milling the raw fiber so as to reduce the diameter of the fiber clumps to less than 300 μm. Properties of composites made with ball-milled material were improved in every respect. VGCF reinforcement in nylon slightly improved the tensile strength and doubled the modulus, while VGCF in polypropylene doubled the tensile strength and quadrupled the modulus compared to unreinforced material. Moreover, the composites were sufficiently improved that differences in fiber surface preparation became important. For example, air-etched fibers and fibers covered with low concentrations of aromatics produced polypropylene composites with significantly better mechanical properties than did fibers whose surfaces were heavily coated with aromatics. Both the tensile strength and the modulus of the composites fabricated with clean fibers exceeded theoretical values for composites made with fibers randomly oriented in three dimensions, indicating that the injection-molding process oriented the fibers to some extent.

Adsorption Studies of Methane Films on Catalytic Carbon Nanotubes and on Carbon Filaments

Adsorption measurements of CH4 on catalytically produced carbon nanotubes were used to determine the wetting behavior of the films, the presence of capillary condensation, and the specific surface area of the tubes. Two groups of carbon tubes were produced. The set of larger tubes had inner diameters on the order of 1 μm, while the set of narrower tubes had inner diameters on the order of 10−100 nm. The narrower carbon tubes were either oxidized in nitric acid, or subjected to high-temperature treatment at 2400 °C in vacuum, or left in as-produced condition. The activation processes were used to open the ends of the tubes. Surface area determinations for untreated and treated tubes established that the specific surface area increased as a result of activation. Isothermal adsorption−desorption cycles were measured on treated and untreated tubes. Hysteresis loops, indicative of the formation of a capillary condensate on the substrate, were present only for the open-ended treated tubes; no hysteresis loops w...

Creep and rupture of an advanced CVD SiC fiber

In the as-produced condition the room temperature strength (~6 GPa) of Textron Specialty Materials' 50 μm CVD SiC fiber represents the highest value thus far obtained for commercially produced polycrystalline SiC fibers. To understand whether this strength can be maintained after composite processing conditions, high temperature studies were performed on the effects of time, stress, and environment on 1400 °C tensile creep strain and stress rupture on as-produced, chemically vapor deposited SiC fibers. Creep strain results were consistent, allowing an evaluation of time and stress effects. Test environment had no influence on creep strain but 1 hour annealing at 1600 °C in argon gas significantly reduced the total creep strain and increased the stress dependence. This is attributed to changes in the free carbon morphology and its distribution within the CVD SiC fiber. For the as-produced and annealed fibers, strength at 1400 °C was found to decrease from a fast fracture value of 2 GPa to a 100-hour rupture strength value of 0.8 GPa. In addition a loss of fast fracture strength from 6 GPa is attributed to thermally induced changes in the outer carbon coating and microstructure. Scatter in rupture times made a definitive analysis of environmental and annealing effects on creep strength difficult.

Experimental and theoretical assessment of the longitudinal tensile strength of unidirectional SiC-fiber/titanium-matrix composites

The tensile strength of unidirectional SiC-fiber/titanium composites (SCS-6/Ti-1100) of varying fiber volume fraction (0.15–0.35) was measured in the as-produced condition. Additionally, fibers were etched from the panels and tensile tested to determine their strength distribution, interface properties were measured with fiber push-out tests, and the tensile properties of the matrix (without fiber) were also determined. From the measured constituent properties, the composite strength was predicted by using both global and local load-sharing (GLS and LLS) models, and these predictions were compared with the measured values. The composite strength was lower than predicted by Curtin's GLS model, but greater than predicted if it is assumed that the first fiber failure initiates composite failure (i.e. severe LLS). Metallographic examination of the fractured specimens revealed that the failure was consistent with a non-cumulative (localized damage) failure mode, which, as suggested by previous theoretical and experimental studies, is promoted by matrix plasticity.

Morphology of melt-spun silicon alloy ribbons

Morphological investigations have been performed on melt-spun ribbons of silicon-based binary alloys containing aluminium, copper, cobalt and vanadium. Additions of strontium and phosphorus were made to the aluminium and copper alloys to find that structure modification effects at high cooling rates are indicated. The ribbons 50 μm thick and 2–3 mm wide were prepared by induction melting and copper die casting and subsequent melt spinning under an inert atmosphere. The primary silicon crystals were identified as typically 5 μm equiaxed dendritic or 20 μm columnar dendritic faceted crystals embedded in eutectic. High silicon content ribbons exhibit more dendritic silicon crystals than low silicon content ribbons did. All melt-spun ribbons were brittle in the as-produced condition.

真空圧延接合法によるクラッド材の製造とその特性 （第２報） アルミニウムクラッド鋼の接合界面特性に及ぼす加熱処理の影響

An aluminum clad steel was produced using the vacuum roll bonding. The clad steel was heated at 560 to 650°C for 0 to 20 s to study formation of intermetallic phases and bond shear strength in the bond interface between the aluminum and the steel of the aluminum clad steel given weld thermal cycles. Main results obtained are as follows ; (1) Although the clad steel was heated at 650°C without holding, an intermetallic phase was not formed in the bond interface. (2) However, when the clad steel was heated for a certain time, intermetallic phases of FeAl3 and Fe2Al5 were formed in the bond interface and the activation energy for formation of the phases was 41 kcal/mot. (3) When the thickness of the phases was more than around 1.5μm, the bond shear strength of the clad metal was abruptly decreased in comparison with that of the clad steel in as-produced condition.

Microstructure of Rapidly Solidified Ti3Al Alloys

ABSTRACTThe microstructures of ordered Ti3Al-lZr (alpha2 +Zr) and Ti-Al-Nb alloys produced by ingot metallurgy (IM) and by rapid solidification (RS) are compared. The RS Ti3Al-iZr (alpha2 structure) alloy displayed small antiphase domains (APD) of 10–20 nm in the as-produced condition, but large grain size. The latter observation is rationalized in terms of the cooling history used to produce the material. The RS Ti-Al-Nb alloy exhibited an equiaxed microstructure. The IM Ti-Al-Nb material displays a complete change in microstructure between 1010°C and 1035°C, indicating a narrow alpha+beta phase field.

Effect of Solution Heat-Treatment on the Corrosion Behaviour of an Al–Ti–Brass (TIBRAL)

The resistance of Al–Ti–brass to generalised corrosion in sea water was studied, both in its as-produced condition, and also after suitable solution heat-treatment, by means of polarisation curves and measurements of polarisation resistance, Rp. In both stagnant and flowing sea water the alloy, in the asproduced state, showed better resistance than Cu–Ni/90–10 and was comparable with Al–brass. The resistance was even better after solution heat-treatment.