1,721,226 research outputs found
Dry sliding wear of an induction-hardened, high-silicon medium-carbon microalloyed steel
No full textMicroalloyed (MA) medium carbon steels are promising materials as a replacement of
quenched and tempered (Q-T) grades. The dry sliding behaviour of an induction hardened medium
carbon MA steel, compared to Q-T steel, in the same surface hardening condition, was investigated. The
MA steel showed a higher frictional stability and wear resistance than the Q-T steel. The transition
from the mild oxidative wear regime to the severe adhesive wear regime occurred under more severe
sliding condition for the MA steel. This can be ascribed the superior hardness of the bulk material and
also to its higher tempering stability, induced by the strengthening precipitates, that enhance the load
bearing capacity of the MA steel and hence the stability protective oxide layers
Microstructural and mechanical properties characterization of heat treated and overaged cast A354 alloy with various SDAS at room and elevated temperature
No full textThe aim of the present study was to carry out a microstructural and mechanical characterization of the A354 (Al-Si-Cu-Mg) cast aluminum alloy. The effect of microstructure on the tensile behaviour was evaluated by testing samples with different Secondary Dendrite Arm Spacing, (SDAS) values (20-25 μm and 50-70 μm for fine and coarse microstructure, respectively), which were produced through controlled casting conditions. The tensile behaviour of the alloy was evaluated both at room and elevated temperature (200 °C), in the heat treated and overaged (exposure at 210 °C for 41 h, after solution heat treatment) conditions. Optical, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were used for microstructural investigations.
Experimental data confirmed the significant role of microstructural coarseness on the tensile behaviour of A354 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Moreover, solidification rate influenced other microstructural features, such as the eutectic silicon morphology as well as the size of the intermetallic phases, which in turn also influenced elongation to failure. Coarsening of the strengthening precipitates was induced by overaging, as observed by STEM analyses, thus leading to a strong reduction of the tensile strength of the alloy, regardless of SDAS. Tensile properties of the alloy sensibly decrease at elevated temperature (200 °C) in all the investigated heat treatment conditions
Effect of Mo Addition on Room and High Temperature Tensile Behavior of Al-Si-Cu-Mg Alloy in As-Cast and Heat-Treated Conditions
No full textThis study focuses on the role of Mo addition on the mechanical properties of an Al-Si-Cu-Mg alloy in as-cast and heat-treated condition at ambient and elevated temperature. Addition of 0.4 to 0.6 wt.% Mo forms Mo-bearing dispersoid particles which have a relatively high melting point and improve high temperature tensile strength. Ductility suffered in the presence of Mo-bearing particles. Trace addition of Mo up to 0.6 wt.% has a negligible influence on the yield strength and hardness of Al-Si-Cu-Mg alloy in as-cast and heat-treated conditions at ambient temperature and 250 °C
Laser Powder Bed-Fused Scalmalloy®: Effect of Long Thermal Aging on Hardness and Electrical Conductivity
Full text linkThis study investigates the microstructural evolution, porosity characteristics, and mechanical behavior of LPBF-manufactured Scalmalloy®, which were investigated in the as-built conditions and after long-term exposure to direct aging of 275, 325, and 400 °C. Optical microscopy, and electron backscatter diffraction (EBSD) analyses were employed to examine the grain morphology, pore distribution, and defect characteristics. In the as-built state, the microstructure displayed the typical fish-scale melt pool morphology with columnar grains in the melt pool centers and fine equiaxed grains along their boundaries, combined with a small number of gas pores and lack-of-fusion defects. After direct aging, coarsening of grains was revealed, accompanied by partial spheroidization of pores, though the global density remained above 99.7%, ensuring structural integrity. Grain orientation analyses revealed a reduction in crystallographic texture and local misorientation after direct aging, suggesting stress relaxation and a more homogeneous microstructure. The hardness distribution reflected this transition: in the as-built state, higher hardness values were found at melt pool edges, while coarser central grains exhibited lower hardness. After direct aging, the hardness differences between these regions decreased, and the average hardness increased from (104 ± 7) HV0.025 to (170 ± 10) HV0.025 due to precipitation of Al3(Sc,Zr) phases. Long-term aging studies confirmed the stability of mechanical performance at 325 °C, whereas aging at 400 °C induced overaging and hardness loss due to precipitate coarsening. Electrical conductivities increased monotonically at all tested temperatures from ~11.7 MS/m, highlighting the interplay between solute depletion and precipitate evolution
Replacement of Nitrided 33CrMoV Steel with ESR Hot Work Tool Steels for Motorsport Applications: Microstructural and Fatigue Characterization
No full textIn this work tensile strength, fatigue resistance and fracture toughness of two electroslag remelted (ESR) tool steels and of 33CrMoV12 ESR steel (both in quenched and tempered condition, as well as nitrided condition) were evaluated. The role of hardness, residual stresses and inclusion sizes on the fatigue behavior was investigated. Tool steels have a tensile strength between about 1900 and 2300 MPa, fracture toughness between 35 and 33 MPa root m, while fatigue strength ranges between 725 and 992 MPa. The tensile strength and fracture toughness of the 33CrMoV12 ESR are, respectively, 1365 MPa and about 150 MPa root m. Nitriding induces a significant increase in fatigue strength from 560 to 980 MPa. These results highlight that appropriate ESR tool steels could replace nitrided steels
Effect of heat treatment on microstructure and mechanical properties of a Fe-12.2Cr-10Ni-1Mo-1Ti-0.6Al precipitation hardening-stainless steel manufactured via laser powder bed fusion
No full textPrecipitation hardening-stainless steels (PH-SS) can be easily manufactured by laser powder bed fusion (LPBF) and hardened to high strength, enabling the production of molds and dies featuring conformal cooling channels with no cracks, high strength, and corrosion resistance. Previous works showed that LPBF-manufactured PH-SS can be strengthened through a one-step direct aging (DA) treatment, instead of the traditional solution annealing and aging (SA), with cost, time, and energy consumption reduction. However, significant differences remain between the microstructures of DA- and SA-treated parts, potentially affecting the resulting mechanical behavior. The present work investigates the microstructure and the mechanical behavior of a PH-SS manufactured by LPBF, AMPO M789, in the as-built (AB) condition and after SA and DA heat treatments. Compared to the AB state, both heat treatments led to a great increment of hardness (from ~ 320 HV to 570–585 HV), yield strength (152–164%) and tensile strength (76–84%) together with a reduction of ductility (31–46%) and impact toughness (93–95%). However, DA led to significantly higher ductility (+ 29%) and toughness (+ 25%) than SA despite a strength reduction of only 5% and a similar hardness. The better strength–ductility balance of DA was attributed to a higher austenite content (~ 8% vs. ~ 3%) and to the oriented microstructure resulting from LPBF, retained by DA and recovered by SA, which limited the cleavage fracture mode thus promoting a ductile behavior. Results indicated the feasibility of DA to replace SA for LPBF-manufactured PH-SS in industrial applications
Mechanical Performance of Nodular Cast Irons After Prolonged High-Temperature Exposure
No full textDuctile cast irons (DIs) are widely used in industrial applications. Their use is, however, often limited to components working at room temperature, since prolonged exposure at high temperature can lead to decomposition of both ausferrite and pearlite, with a consequent strength reduction. The present paper evaluated the effects of prolonged high-temperature exposure on microstructure and residual strength of DIs with different matrices, after an isothermal soaking at temperatures between 200 and 600 °C. Microstructural analyses highlighted that long-term exposure at temperatures higher than 500 °C leads to the complete decomposition of ausferritic and pearlitic matrix microstructures, while hardness tests showed that the hardness is stable up to 500 °C for the pearlitic ductile iron (PDI), up to 450-500 °C for the ausferritic ductile iron (ADI) and up to 400-450 °C for the perferritic isothermed ductile iron (IDI). Exposure at 500 °C for 240 h induces a reduction in tensile strength of IDI and ADI, respectively, of 10 and 25% (for both room temperature and 500 °C tensile testing), while it has no significant effects on PDI
Aging Behaviour of a 12.2Cr-10Ni-1Mo-1Ti-0.6Al Precipitation-Hardening Stainless Steel Manufactured via Laser Powder Bed Fusion
Full text linkThe combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed
Predictive equations of the tensile properties based on alloy hardness and microstructure for an A356 gravity die cast cylinder head
No full textExcellent castability and high strength-to-weight ratio, which increases performance and fuel economy, have made A356 alloy one of the most suitable materials for various applications in the
automotive industry, such as cylinder head and engine block. The main limitation of cast Al-Si alloys is, however, the considerable influence of the solidification and heat treatment conditions on the final microstructure and consequently on the mechanical properties, that can thus exhibit a wide range of variability in the same cast component. Literature data often relate the static and fatigue properties of cast Al alloys to only one microstructural parameter, such as solidification defects or secondary dendrite arm spacing, without taking into account their simultaneous effect. In addition, the experimental tensile and fatigue data are often obtained on specimens cast apart or obtained under controlled laboratory conditions, substantially different from those of industrial cast components. For these reasons, the main problem in the design phase is the lack of knowledge of the true local mechanical properties, that often make a very conservative approach necessary, with a consequent increase of the cross sections and consequently of the weight. The aim of this research was to study a
complex cast component, produced under industrial conditions, in order to verify the range of variability of the microstructural parameters and the tensile properties. The component was an A356
gravity die cast cylinder head, heat treated at the T6 condition, and the effect of the delay between quenching and aging on the alloy hardness was also evaluated. Mathematical models, able to
successfully predict the local tensile properties in the cast, from the concurrent effect of the main microstructural parameters and alloy hardness, are proposed. These models allow the designer to
predict the local tensile behaviour, without any tensile tests, and can link the post-processing results of the casting simulation software to the pre-processing phase of the structural ones, with an approach of co-engineered design
Linearising anhysteretic magnetisation curves: A novel algorithm for finding simulation parameters and magnetic moments
Full text linkThis paper proposes a new method for determining the simulation parameters of the Jiles–Atherton Model used to simulate the first magnetisation curve and hysteresis loop in ferromagnetic materials. The Jiles–Atherton Model is an important tool in engineering applications due to its relatively simple differential formulation. However, determining the simulation parameters for the anhysteretic curve is challenging. Several methods have been proposed, primarily based on mathematical aspects of the anhysteretic and first magnetisation curves and hysteresis loops. This paper focuses on finding the magnetic moments of the material, which are used to define the simulation parameters for its anhysteretic curve. The proposed method involves using the susceptibility of the material and a linear approximation of a paramagnet to find the magnetic moments. The simulation parameters can then be found based on the magnetic moments. The method is validated theoretically and experimentally and offers a more physical approach to finding simulation parameters for the anhysteretic curve and a simplified way of determining the magnetic moments of the material
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