The aging Al–Zn–Mg–Cu alloy exhibits a significant decrease in performance after undergoing thermal shock. In order to improve the resistance of this type of alloy to thermal shocks, the influence of ...deep cryogenic treatment (DCT) on the high temperature mechanical properties and microstructure of thermal shocked Al–Zn–Mg–Cu alloy is investigated in this paper. It was found that the mechanical properties of Al–Zn–Mg–Cu alloys decrease significantly with the increase of electric heating temperature. The deep cryogenic treatment reduced the grain size of Al–Zn–Mg–Cu alloy, increased the density of the precipitates, and also inhibited the coarsening of the precipitates. Therefore, the deep cryogenic treatment can slow down the weakening effect of Al–Zn–Mg–Cu alloy at high temperatures.
Deep cryogenic treatment of tool steels Podgornik, B.; Paulin, I.; Zajec, B. ...
Journal of materials processing technology,
03/2016, Letnik:
229
Journal Article
Recenzirano
The aim of our research work was to investigate the effect of deep cryogenic treatment on fracture toughness, wear resistance and load-carrying capacity of cold work tool steel and to determine the ...effectiveness of deep cryogenic treatment depending on the tool steel type and chemical composition. The type and chemical composition of the tool steel considerably affect the way how deep cryogenic treatment changes mechanical, tribological and load-carrying capacity of the tool steel. For lower carbon and higher W and Co containing cold work tool steel properties can be improved for up to 70%, but are very limited in the case of high-speed steel. At high carbon and vanadium contents properties of cold work tool steels can even be deteriorated after deep cryogenic treatment. In terms of abrasive wear resistance and load-carrying capacity increasing the hardness is the most decisive factor.
The cryogenic treatment of near β Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531) alloy was conducted using the liquid nitrogen refrigeration method. The microstructure and properties were characterized by scanning ...electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results show that the alloy achieves optimal properties at a cryogenic time of 8h. Compared to samples that were not cryogenically treated, microhardness, ultimate tensile strength (UTS), and elongation increased by 12.9%, 6.8%, and 8.0% respectively. Detailed microstructural characterization indicated that the cryogenic processing can lead to grain refinement, enhanced dislocation density, and accelerate the transformation of the metastable β phase into the stable α phase, resulting in a higher volume fraction of the α phase. After cryogenic treatment, the lath-shaped α phase reorients from a vertical to a parallel orientation, and its average width is reduced. Simultaneously, cryogenic treatment diminished texture strength but enhanced the uniformity of the alloy. Improvements induced by cryogenic treatment are attributed to alloy volume and lattice contraction caused by cold compression forces at cryogenic temperatures, which generate internal stress and grain deflection.
The deterioration of fluid machines due to slurry and cavitation erosion significantly impairs their serviceability. In the present work, we investigated the influence of deep cryogenic treatment ...(DCT) on the slurry and cavitation erosion resistance of WC-10Co-4Cr coatings developed using the detonation spraying technique. For comparison, hydroturbine steels and other conventional (Alumina and Stellite 6) coatings were also investigated. All thermal spray coatings showed typical lamellar structure along with the presence of pores and splat boundaries. Among all the coatings, the WC-10Co-4Cr showed the highest slurry (up to 15 times) and cavitation (2 times) erosion resistance owing to high hardness and fracture toughness. Post DCT, the WC-10Co-4Cr coating showed further improvement due to reduced porosity and improved hardness without decrement in fracture toughness. As a result, the DCT coating showed 1.5 to 4.2 times improved slurry erosion resistance than the as-sprayed counterpart, along with 1.6 times higher cavitation erosion resistance. The improved tribological performance of the coating after DCT is associated with enhanced hardness due to the presence of nano precipitates and densification as analyzed using electrochemical techniques. The topological analysis of the eroded surfaces indicated micro-cutting, micro-cracking, and delamination as the primary mechanism controlling the erosion behavior of the coatings.
•DCT of WC-10Co-4Cr coating performed for hydroturbine applications.•The DCT resulted in densification with reduced porosity.•DCT resulted in increased hardness of coating without lowering the toughness.•The slurry erosion resistance of the coating post DCT improved by 4 times.•The cavitation erosion resistance of the coating increased by 60%.
•A feasible strategy was suggested to produce “finer grains + high-density TBs + precipitates” architectures in LPBF-fabricated Inconel 718.•A favorable strength and excellent plasticity (1088 MPa, ...1369 MPa, 30 %) was obtained.•The intensive interactions between GBs/TBs/precipitates and dislocations under finer grain scale offers a strong strain hardening effect.•Deformation modes of SFs, L-C locks, primary DTs, and secondary twins sustaining an additional and higher strain hardening rate.
Tailoring high-density annealing twins in laser powder bed fusion (LPBF)-fabricated alloys based on their intrinsic residual stress requires high annealing temperatures and/or long-term annealing, resulting in the abnormal growth of large recrystallized grains, which is detrimental to mechanical properties. This work proposes a new strategy for achieving a favorable strength–plasticity synergy of the LPBF-fabricated Inconel 718 superalloy by performing a deep cryogenic treatment (DCT) with the subsequent heat treatment (including annealing and double aging) to tailor fine grains with “high-density annealing twins + precipitates” architectures and compares the obtained material with an alloy subjected to a direct heat treatment without a prior DCT. The obtained results reveal that the additional internal stress generated during DCT increases the stored energy and dislocation density, which provide a sufficient driving force for activating high-density annealing twin boundaries (63.2 %) with fine grains (31.6 μm) within a short annealing time. The more homogeneous tailored microstructure with the “finer grains + high-density twins + precipitates” architectures decreases the mean free path of slipping dislocations, promoting intensive interactions with dislocations and inducing a strong strain hardening effect. The multiple deformation modes of stacking faults coupled with Lomer–Cottrell locks, thin primary deformation twins, and secondary twins activated during tensile loading, sustaining a strong work hardening ability and delaying the plastic instability, which exhibits a high strength (yield strength of 1088 MPa and tensile strength of 1369 MPa) and excellent plasticity (elongation of 30 %). This work not only describes a feasible method for simultaneously enhancing the strength and plasticity in additively manufactured (AM) alloys but also provides new insights into increasing the fraction of twins at a small grain size to improve the grain boundary-related properties without destroying the AM alloy shape.
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A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by ...tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life.
To simultaneously improve the mechanical properties and corrosion resistance of AA2024 aluminum alloy, a T8I4 with deep cryogenic treatment (DCT) process is proposed, which includes solution ...heat-treatment, cold-drawing deformation, pre-aging, DCT and re-aging. The microstructure of AA2024 is observed by confocal laser scanning microscope, scanning electron microscopy and transmission electron microscopy. The properties of AA2024 are studied by hardness measurement, tensile test, friction and wear test, exfoliation corrosion test, intergranular corrosion test and electrochemical corrosion test. On comparison with T6, AA2024-T8I4 +DCT obviously increases its hardness, tensile strength and wear resistance. AA2024-T8I4 +DCT has similar corrosion resistance to T7X two-stage aging. According to comprehensive analysis, the MPts in AA2024-T8I4 +DCT with 3 % deformation amount have the maximum pinning force to the dislocations, and the alloy has the largest hardness, strength and the best wear resistance. The discontinuous grain boundary precipitates in AA2024-T8I4 +DCT with 1 % deformation amount are discontinuous and fine, and the precipitate free zone is not obvious, which makes the corrosion difficult to develop. The alloy has the shallowest intergranular corrosion depth, the smallest corrosion rate and the best corrosion resistance
•T8I4 with deep cryogenic treatment make AA2024 have better comprehensive properties.•Precipitates have the pinning force to the dislocation introduced by cold deformation.•Larger deformation amount results in more and coarser matrix precipitates in same aged alloy.•The grain boundary precipitates are discontinuous in T8I4 with deep cryogenic treated AA2024.•Narrower precipitate free zone is conducive to better corrosion resistance of AA2024.
In the mass production of automotive parts, the tool life of the manufacturing tool is very important from an economic site. The tool life is determined by the material quality and the properties of ...the tool achieved by heat treatment. Böhler K340 Isodur grade tool steel is considered one of the best cold forming tool steels due to its chemical composition and its electro-slag remelting manufacturing. In our experiments, samples made from this steel were subjected to two different heat treatment technologies. The first one (CT-conventional treatment) was tempered three times at high temperature after high temperature hardening, and the second one (DCT-deep cryogenic treatment) was deep frozen – with nitrogen – after high temperature hardening and then tempered three times at high temperature. After the heat treatment, the pieces were subjected to microscopic, toughness, hardness and wear tests. The results of the measurements showed that the structure of the DCT steel is much finer and more homogeneous than the CT steel, the impact strength is higher, there is no difference in hardness, but the wear resistance of the CDP specimen is better than the CT specimen.
This study investigates the impact of deep cryogenic treatment (DCT) on microstructure and properties of a martensitic stainless steel AISI 431. The reasonably simplistic microstructure tailoring ...with DCT delivers a novel pathway towards advanced 3rd generation high-strength steels (AHSS), whilst utilizing existing alloys and chemistry. The resulting microstructural changes deliver improved strength and hardness of the material, whilst still sustaining good elongation properties. DCT reduces the material's toughness but improves its deformation resistance and wear resistance. The study reveals that DCT modifies the microstructural evolution during tempering. During the conventional treatment, AISI 431 develops austenite reversion transformation (ART), which allows the high strength and elongation capabilities formed with transformation-induced plasticity (TRIP). In contrast, DCT progresses the microstructure even further by retransforming the reverted austenite formed through ART into tertiary α-martensite, ε-martensite and carbides that increase the strength and deformation behavior of AISI 431. The novel microstructural modification that we have entitled cryogenic austenite retransformation (CAR), is both experimentally and theoretically assessed. The underlying transformation mechanisms of CAR and individual stages of DCT were evaluated with ex-situ electron backscatter diffraction and transmission electron microscopy. The impact of DCT on the modified transformation capabilities of AISI 431 is discussed in relation to possible implementation in automotive industry as a universally applicable treatment procedure.
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•Deep cryogenic treatment (DCT) modifies the microstructure of AISI 431.•Transformation of reverted austenite is progressed with tempering after DCT.•DCT modifies tensile response, wear resistance and fracture mechanism of AISI 431.•DCT allows novel combination of properties and microstructure tailoring.•Properly treated AISI 431 has potential as a new candidate of next generation AHSS.
Here, a new strategy, i.e., laser shock peening (LSP) followed by cyclic deep cryogenic treatment (DCT), is proposed to generate the gradient hierarchical structures and thus promote ...strength-ductility synergy of a high entropy alloy (HEA). We show that the non-equiatomic CrFeCoNiMn0.75Cu0.25 HEA sample treated by this new strategy possesses an excellent combination of high strength (∼1100 MPa) and high plasticity (30%). Higher yield strength is achieved in HEA samples treated by LSP, due to the introduction of a gradient microstructure comprising sub-grains, dense dislocations and nano-twins (NTs) near the treated surface. Then, the following cyclic DCT processing can further introduce various types of reinforcing defect microstructures in core region of LSP-treated HEA, including dense intersecting NTs and stacking faults, thus effectively improving the tensile strength and plasticity. These results obtained here can shed new insights into develop high performance HEAs by tailoring residual stress and generating optimized microstructures.
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