Heavy duty (HD) vehicles are projected to be the largest fuel-use subsector in transportation, with current demand for diesel fuel projected to grow 30% by 2040. Historically, a primary strategy for ...increasing diesel engine efficiency has been to increase peak cylinder pressure (PCP). However, increasing PCP imparts greater mechanical and thermal loads on engine components and materials. In recent years, the material property limits for many components have been reached and further increases in PCP above ∼20 MPa have been difficult, while still maintaining the necessary affordability and longevity of on-road HD diesel engines. This paper reviews the historical evolution and major metallurgical advancements of high temperature materials in HD on road diesel engines (10–15 L displacement) up to the current state of the art, focusing on materials in the engine block, cylinder heads, pistons, valves, and exhaust components. These components cover a wide range of material classes, including cast iron, ferritic steel, austenitic steel, titanium alloys, nickel based super-alloys, and high temperature coatings. The microstructural degradation and failure mechanisms of the materials associated with the complex mechanical and thermal loading during service are discussed and key areas for future materials research are suggested that overcome technical barriers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
While the strengthening of Al-Cu alloys due to precipitation has been extensively studied, the effect of crystallographic orientation of the matrix and precipitates, as well as precipitate ...morphology, on the strain hardening behavior is not well understood. Here we investigate this effect with in situ neutron diffraction during deformation of an Al-Cu alloy (206) after multiple aging treatments. Precipitate-dislocation interactions were found to change from precipitate shearing for microstructures predominantly containing GPI and θ′′ precipitates to Orowan looping for microstructures with primarily θ′ and θ precipitates. Notably, significant anisotropy in strain hardening behavior was observed when θ′ precipitates were present, which was attributed to crystallographic orientation dependent load transfer from the Al matrix to the θ′ precipitates. The anisotropic load transfer is hypothesized to be caused by the extent of rotation of high aspect-ratio θ′ precipitates, owing to dislocations looping around them during plastic deformation of the matrix. Predictions from an analytical model describing the anisotropic magnitude of load transfer from precipitate rotation agree well with experimental results, successfully validating the precipitate rotation hypothesis and explaining the anisotropic strain hardening behavior. This model allows for the prediction of stresses separately in the precipitate and matrix phases as a function of crystallographic orientation, only given the bulk mechanical properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fracture toughness of thermal barrier coatings (TBCs) has gained significant interest in recent years as one of the dominant design parameters dictating selection of materials and assessing ...durability. Much progress has been made in characterizing and understanding fracture toughness of relevant TBC compositions in their bulk form, but it is also apparent that the toughness is significantly affected by process‐induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma‐sprayed TBCs has been carried out. Yttria partially stabilized zirconia (YSZ) coatings were fabricated under different process conditions inducing different levels of porosity and defect densities. Fracture toughness was measured on free‐standing coatings in as‐processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative composition, Gd2Zr2O7 which, as anticipated, shows significantly lower fracture toughness compared to YSZ. The results not only point toward a need for process and microstructure optimization for enhancing TBC performance, but also a framework for establishing performance metrics for promising new TBC compositions.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
An Al–Cu alloy micro-alloyed with Mn and Zr (ACMZ) was examined to understand the thermal stability and strengthening mechanism of metastable θ'-Al2Cu precipitates with interfacial segregation after ...prolonged thermal exposure. The microstructure was characterized at multiple scales with techniques including synchrotron x-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, and atom probe tomography. The θ' precipitates did not exhibit measurable coarsening after thermal exposure at 300°C for 5000 h. Kinetic effects of Mn and Zr interfacial segregation, which dominate over thermodynamic effects under these conditions, were necessary to understand the complete inhibition of precipitate coarsening. The θ' phase fraction was stable during the 5000 h exposure. This stable phase fraction was regarded as the metastable equilibrium value and was smaller than that predicted by the θ' solvus line of the ACMZ alloy. As expected from the observed phase stability, the alloy hardness also remained stable during the 5000 h exposure. An Orowan mechanism alone was inadequate to explain θ' precipitate strengthening. Additional strengthening mechanisms by θ' precipitates specifically related to the transformation strain may explain the observed hardness values.
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•Metastable θ'-Al2Cu precipitates are coarsening resistant at 300 °C for 5000 h in an Al-Cu-Mn-Zr alloy.•Metastable equilibrium θ' phase fraction is lower than the prediction using the θ' solvus line.•Hardness remains stable during the 5000 h thermal exposure.•Orowan strengthening from θ' precipitates is inadequate to explain the alloy hardness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Lattice mismatch modeling of aluminum alloys Shin, Dongwon; Roy, Shibayan; Watkins, Thomas R. ...
Computational materials science,
October 2017, 2017-10-00, 2017-10-01, Volume:
138, Issue:
C
Journal Article
Peer reviewed
Open access
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We present a theoretical framework to accurately predict the lattice mismatch between the fcc matrix and precipitates in the multi-component aluminum alloys as a function of ...temperature and composition. We use a computational thermodynamic approach to model the lattice parameters of the multi-component fcc solid solution and θ′-Al2Cu precipitate phase. Better agreement between the predicted lattice parameters of fcc aluminum in five commercial alloys (206, 319, 356, A356, and A356+0.5Cu) and experimental data from the synchrotron X-ray diffraction (SXD) has been obtained when simulating supersaturated rather than equilibrium solid solutions. We use the thermal expansion coefficient of thermodynamically stable θ-Al2Cu to describe temperature-dependent lattice parameters of meta-stable θ′ and to show good agreement with the SXD data. Both coherent and semi-coherent interface mismatches between the fcc aluminum matrix and θ′ in Al-Cu alloys are presented as a function of temperature. Our calculation results show that the concentration of solute atoms, particularly Cu, in the matrix greatly affects the lattice mismatch.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The first part of this study documented the as-aged microstructure of five cast aluminum alloys namely, 206, 319, 356, A356, and A356+0.5Cu, that are used for manufacturing automotive cylinder heads ...(Roy
et al.
in Metall Mater Trans A,
2016
). In the present part, we report the mechanical response of these alloys after they have been subjected to various levels of thermal exposure. In addition, the thermophysical properties of these alloys are also reported over a wide temperature range. The hardness variation due to extended thermal exposure is related to the evolution of the nano-scale strengthening precipitates for different alloy systems (Al-Cu, Al-Si-Cu, and Al-Si). The effect of strengthening precipitates (size and number density) on the mechanical response is most obvious in the as-aged condition, which is quantitatively demonstrated by implementing a strength model. Significant coarsening of precipitates from long-term heat treatment removes the strengthening efficiency of the nano-scale precipitates for all these alloys systems. Thermal conductivity of the alloys evolve in an inverse manner with precipitate coarsening compared to the strength, and the implications of the same for the durability of cylinder heads are noted.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A356/316 L interpenetrating phase composites can be fabricated by infiltrating additively-manufactured 316 L stainless-steel lattices with a molten A356 aluminum alloy, a new process termed ...PrintCasting. This work investigates the mechanical properties of PrintCast composites and their relation to the volume-fraction of 316 L reinforcement. Uniaxial tension experiments were conducted with A356/316 L PrintCast composites that had either 30 vol%, 40 vol% or 50 vol% 316 L. When 316 L reinforcement increased from 30 vol% to 40 vol%, a > 200% increase in ductility and 400% increase in absorbed-energy were observed, while a much lower increase was exhibited when reinforcement increased from 40 vol% to 50 vol%. The failure of the 30 vol% sample occurred by localized deformation and a single failure initiation region, in contrast to the 40 vol% and 50 vol% samples which failed by delocalized damage in the entire gauge section. To understand this transition phenomena, digital image correlation (DIC) was coupled with finite element (FE) analysis to capture the deformation and failure processes. The results revealed that, for all samples, stress concentrated and failure initiated in a 316 L strut near the lattice nodes, where the strut underwent localized bending-dominated deformation. In the high 316 L volume-fraction composites, the increase in 316 L-strut diameter reduced local bending stress and stabilized the deformation, leading to improved damage tolerance. Based on the presented analysis, local modifications to the PrintCast structure are suggested.
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•Combining directed energy based additive manufacturing with metal casting to create metallic constituent composites.•Additively-manufactured 316 L lattices infiltrated with molten A356•Transition from localized deformation and fracture to delocalized damage with increase of 316 L•Coupled digital image correlation and finite element analysis
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The present study stages a comparative evaluation of microstructure and associated mechanical and thermal response for common cast aluminum alloys that are used for manufacturing automotive cylinder ...heads. The systems considered are Al-Cu (206-T6), Al-Si-Cu (319-T7), and Al-Si (356-T6, A356-T6, and A356 + 0.5Cu-T6). The focus of the present manuscript is on the evaluation of microstructure at various length scales after aging, while the second manuscript will deal with the mechanical and thermal response of these alloys due to short-term (aging) and long-term (pre-conditioning) heat treatments. At the grain-scale, the Al-Cu alloy possessed an equiaxed microstructure as opposed to the dendritic structure for the Al-Si-Cu or Al-Si alloys which is related to the individual solidification conditions for these alloy systems. The composition and morphology of intermetallic precipitates within the grain and at the grain/dendritic boundary are dictated by the alloy chemistry, solidification, and heat treatment conditions. At the nanoscale, these alloys contain various metastable strengthening precipitates (GPI and
θ
″
in Al-Cu alloy,
θ
′
in Al-Si-Cu alloy, and
β
′
in Al-Si alloys) with varying size, morphology, coherency, and thermal stability.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Recent progress in high-performance computing and data informatics has opened up numerous opportunities to aid the design of advanced materials. Herein, we demonstrate a computational workflow that ...includes rapid population of high-fidelity materials datasets via petascale computing and subsequent analyses with modern data science techniques. We use a first-principles approach based on density functional theory to derive the segregation energies of 34 microalloying elements at the coherent and semi-coherent interfaces between the aluminium matrix and the θ′-Al
2
Cu precipitate, which requires several hundred supercell calculations. We also perform extensive correlation analyses to identify materials descriptors that affect the segregation behaviour of solutes at the interfaces. Finally, we show an example of leveraging machine learning techniques to predict segregation energies without performing computationally expensive physics-based simulations. The approach demonstrated in the present work can be applied to any high-temperature alloy system for which key materials data can be obtained using high-performance computing.
Scandium added to Al–Cu–Mg–Ag alloys leads to an in situ phase transformation of coherent Cu-rich nanoprecipitates at elevated temperature, with Sc atoms diffusing and occupying their interstitial ...sites. The transformed nanoprecipitates have enhanced thermal stability while maintaining a large volume fraction and these two microstructural features enable high tensile strength of the Al alloy with creep resistance up to 400 °C.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
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