In the present work,a compressible and lubricating space-holder material commonly known as "acrawax" was used to process Cu foams with various pore sizes and various porosities.The foams were processed witho...In the present work,a compressible and lubricating space-holder material commonly known as "acrawax" was used to process Cu foams with various pore sizes and various porosities.The foams were processed without using binders to avoid contamination of their metal matrices.The lubricant space-holder material was found to facilitate more uniform flow and distribution of metal powder around the surface of the space holder.In addition,the use of acrawax as a space-holder material yielded considerably dense cell walls,which are an essential prerequisite for better material properties.The foams processed with a smaller-sized space holder were found to exhibit better electrical and mechanical properties than those processed with a coarser-sized space holder.The isotropic pore shape,uniform pore distribution throughout the metal matrix,and uniform cell wall thickness were found to enhance the properties pertaining to fine-pore foam samples.The processed foams exhibit properties similar to those of the foams processed through the lost-carbonate sintering process.展开更多
A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treat...A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.展开更多
Aluminum alloys that are additively manufactured using the laser powder bed fusion(LPBF)suffer from relatively poor high cycle fatigue(HCF)resistance.In an effort to alleviate this,a high-strength Al alloy,Al-Mn-Mg-Sc...Aluminum alloys that are additively manufactured using the laser powder bed fusion(LPBF)suffer from relatively poor high cycle fatigue(HCF)resistance.In an effort to alleviate this,a high-strength Al alloy,Al-Mn-Mg-Sc-Zr,with columnar,equiaxed,and bi-modal microstructures was produced by varying the scanning velocity and the substrate temperature during the LPBF process.The tensile strength of LPBF Al-Mn-Mg-Sc-Zr alloy is 475±5–516±6 MPa with favorable elongation of approximately 11%,higher than that of most of the other Al alloys,including conventional high-strength rolled/ECAP Al alloys and AM Al-Mg-Sc-Zr alloys.Specimens with bimodal microstructure and specimens with fully equiaxed microstructure both show a fatigue strength of 230 MPa(at 107 loading cycles),which is the highest among those reported for the LPBF Al alloys.The deformation synergy in the bimodal microstructure also improves the fatigue resistance in the strain-controlled low cycle fatigue(LCF)regime.The equiaxed microstructure restricts the to-and-fro dislocation motion during cyclic loading,which,in turn,minimizes the strain localization.At the later stages of strain accumulation,microcracks form at the grain boundaries,limiting the further improvement of the alloy's fatigue strength.This study demonstrates microstructural tailoring through AM enables improvement of the fatigue resistance of aluminum alloys.展开更多
Generally,data is available abundantly in unlabeled form,and its annotation requires some cost.The labeling,as well as learning cost,can be minimized by learning with the minimum labeled data instances.Active learning...Generally,data is available abundantly in unlabeled form,and its annotation requires some cost.The labeling,as well as learning cost,can be minimized by learning with the minimum labeled data instances.Active learning(AL),learns from a few labeled data instances with the additional facility of querying the labels of instances from an expert annotator or oracle.The active learner uses an instance selection strategy for selecting those critical query instances,which reduce the generalization error as fast as possible.This process results in a refined training dataset,which helps in minimizing the overall cost.The key to the success of AL is query strategies that select the candidate query instances and help the learner in learning a valid hypothesis.This survey reviews AL query strategies for classification,regression,and clustering under the pool-based AL scenario.The query strategies under classification are further divided into:informative-based,representative-based,informative-and representative-based,and others.Also,more advanced query strategies based on reinforcement learning and deep learning,along with query strategies under the realistic environment setting,are presented.After a rigorous mathematical analysis of AL strategies,this work presents a comparative analysis of these strategies.Finally,implementation guide,applications,and challenges of AL are discussed.展开更多
文摘In the present work,a compressible and lubricating space-holder material commonly known as "acrawax" was used to process Cu foams with various pore sizes and various porosities.The foams were processed without using binders to avoid contamination of their metal matrices.The lubricant space-holder material was found to facilitate more uniform flow and distribution of metal powder around the surface of the space holder.In addition,the use of acrawax as a space-holder material yielded considerably dense cell walls,which are an essential prerequisite for better material properties.The foams processed with a smaller-sized space holder were found to exhibit better electrical and mechanical properties than those processed with a coarser-sized space holder.The isotropic pore shape,uniform pore distribution throughout the metal matrix,and uniform cell wall thickness were found to enhance the properties pertaining to fine-pore foam samples.The processed foams exhibit properties similar to those of the foams processed through the lost-carbonate sintering process.
基金supported through the Start-up research grant (No.SRG/2020/000095) of Science and Engineering Research Board,DST,Go INanyang Technological University was supported by the funding from A*STAR via the Structural Metals and Alloys Programme (No.A18B1b0061)+2 种基金Institute of Metal Research CAS was supported by the National Natural Science Foundation of China (Nos.52171164 and 51790484)the National Key Research and Development Program (No.2018YFB0703402)the Youth Innovation Promotion Association CAS (No.2021188)。
文摘A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.
基金the National Natural Science Foundation of China(No.52171026)the Equipment Pre-Research Field Foundation(No.80923010304).
文摘Aluminum alloys that are additively manufactured using the laser powder bed fusion(LPBF)suffer from relatively poor high cycle fatigue(HCF)resistance.In an effort to alleviate this,a high-strength Al alloy,Al-Mn-Mg-Sc-Zr,with columnar,equiaxed,and bi-modal microstructures was produced by varying the scanning velocity and the substrate temperature during the LPBF process.The tensile strength of LPBF Al-Mn-Mg-Sc-Zr alloy is 475±5–516±6 MPa with favorable elongation of approximately 11%,higher than that of most of the other Al alloys,including conventional high-strength rolled/ECAP Al alloys and AM Al-Mg-Sc-Zr alloys.Specimens with bimodal microstructure and specimens with fully equiaxed microstructure both show a fatigue strength of 230 MPa(at 107 loading cycles),which is the highest among those reported for the LPBF Al alloys.The deformation synergy in the bimodal microstructure also improves the fatigue resistance in the strain-controlled low cycle fatigue(LCF)regime.The equiaxed microstructure restricts the to-and-fro dislocation motion during cyclic loading,which,in turn,minimizes the strain localization.At the later stages of strain accumulation,microcracks form at the grain boundaries,limiting the further improvement of the alloy's fatigue strength.This study demonstrates microstructural tailoring through AM enables improvement of the fatigue resistance of aluminum alloys.
文摘Generally,data is available abundantly in unlabeled form,and its annotation requires some cost.The labeling,as well as learning cost,can be minimized by learning with the minimum labeled data instances.Active learning(AL),learns from a few labeled data instances with the additional facility of querying the labels of instances from an expert annotator or oracle.The active learner uses an instance selection strategy for selecting those critical query instances,which reduce the generalization error as fast as possible.This process results in a refined training dataset,which helps in minimizing the overall cost.The key to the success of AL is query strategies that select the candidate query instances and help the learner in learning a valid hypothesis.This survey reviews AL query strategies for classification,regression,and clustering under the pool-based AL scenario.The query strategies under classification are further divided into:informative-based,representative-based,informative-and representative-based,and others.Also,more advanced query strategies based on reinforcement learning and deep learning,along with query strategies under the realistic environment setting,are presented.After a rigorous mathematical analysis of AL strategies,this work presents a comparative analysis of these strategies.Finally,implementation guide,applications,and challenges of AL are discussed.
