- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Microstructure of intercritical heat affected zone and toughness of microalloyed steel laser welds
摘要： Microstructure of laser welds of the X70 low-carbon pipe steel was studied. High cooling rates after laser welding and non-uniform distribution of carbon in the ferrite-pearlite base metal caused formation of regions with increased microhardness (up to 650 НV) in inter-critical heat affected zone (ICHAZ). These regions consisted of finely dispersed degenerate upper bainite and martensite-austenite constituents of a slender shape and small fraction of a massive shape along the boundaries of bainite laths, as well as twinned martensite. High concentration of martensite-austenite constituents (10–16%) and residual stresses in ICHAZ, as well as a dendritic martensitic structure with carbide interlayers along the boundaries of martensite laths in fusion zone were the main reasons of sharp decrease in charpy impact energy of the welded samples. High microhardness of the laser welds was decreased down to 320 HV and their brittleness was improved by annealing. Also, in ICHAZ, degenerate upper bainite and the regions of martensite-austenite constituents decayed forming tempered sorbite and Fe2C and Fe3C carbides, respectively. Charpy impact energy of the welds doubled after annealing compared to the welds without annealing, and ductile-brittle transition temperature decreased down to –60 °С.
关键词： Toughness,Heat affected zone,Structure,Laser welding,Low-carbon steel
更新于2025-09-19 17:13:59
-
Relating fracture toughness to micro-pillar compression response for a laser powder bed additive manufactured bulk metallic glass
摘要： A Zr-based bulk metallic glass produced using selective laser melting (SLM) was compared to the same alloy fabricated using traditional suction-casting. Analysis of the fracture toughness and mechanism through single edge notched beam bending experiments show a significantly reduced damage tolerance for the laser-processed material (KQ ~ 138.0 ± 13.1 → 28.7 ± 3.7 MPa √m), even though X-ray diffraction and microhardness responses were identical. Uncovered here using uniaxial quasistatic micro-pillar compression, as-cast samples more readily undergo shear transformations (evidenced through discrete load drops) below the nominal 0.2% yield stress, which can be connected to the higher macroscopic toughness. Differential scanning calorimetry demonstrated that the increased barrier to shear transformation for the SLM material could not be explained by the relative relaxation states. Rather, it is attributed to the greater dissolved oxygen concentration in the laser-processed material, which is postulated to decrease atomic mobility in the structure and thereby increase the activation energy required to initiate shear transformations.
关键词： fracture toughness,metallic glass,amorphous materials,additive manufacturing,selective laser melting,micromechanics
更新于2025-09-19 17:13:59
-
Microstructure refinement and properties of 1.0C-1.5Cr steel in a duplex treatment combining double quenching and laser surface quenching
摘要： The 1.0C-1.5Cr steel was subjected to conventional quenching and laser surface quenching treatment. A process combing double quenching and laser surface quenching was proposed for enhancing surface hardness and obtaining finer microstructure. The cementite dissolution and grain growth behavior in the austenitizing process of single quenching, double quenching, and laser surface quenching were studied. The results indicated that compared with single quenching, mean diameter of undissolved cementite particles (UCP) was much finer in double quenching, and the final prior austenite grain size (PAGS) could be decreased by nearly 40% to about 4.5 μm. Both grain and cementite particles near the surface will coarsen after laser surface treatment. Compared with single quenching, the PAGS within hardened layer can be decreased by at least 11% through double quenching, and the mean diameter of UCP at the bottom of hardened layer can be decreased by about 20%. Compared with conventional quenching, surface hardness was enhanced by about 20% through laser surface quenching, contributing to the wear resistance. However, the hard and brittle surface layer tends to be crack source during the impact process, leading to the deterioration of final impact toughness. Under the identical laser parameters, the impact absorbed energy is similar in both single and double quenching, which is about 25% of that before laser surface quenching. The impact absorbed energy can be increased from 22J to 28J by preheating at 160 C during the laser surface quenching.
关键词： Impact toughness,Grain size,Cementite,Laser surface quenching,Double quenching,Wear
更新于2025-09-19 17:13:59
-
Effects of Stress-Relieving Heat Treatment on Impact Toughness of Direct Metal Laser Sintering (DMLS)-Produced Ti6Al4V (ELI) Parts
摘要： The impact toughness of as-built (AB) and stressed-relieved (SR) direct metal laser sintering-produced Ti6Al4V (ELI) was investigated using the standard Charpy impact test over the temperature range of ?130°C to 250°C. Stress-relieving heat treatment was conducted at 650°C for a soaking period of 3 h in argon gas atmosphere. The results showed improvements in the impact toughness after stress-relieving heat treatment. Stress relieving also shifted the established ductile-to-brittle transition temperature to lower temperatures. Comparative analysis of the impact toughness values for AB and SR specimens at ambient temperature showed them to be 48% and 22% lower than recommended values for use in aircraft structures, respectively.
关键词： Impact Toughness,Stress-Relieving Heat Treatment,Ti6Al4V (ELI),Direct Metal Laser Sintering,Charpy Impact Test
更新于2025-09-12 10:27:22
-
Experimental Investigations on the Effects of Multicomponent Laser Boriding on steels
摘要： In this investigation, the effects of the multicomponent (Ni+Cr+B4C) laser boriding on the microstructure, microhardness, ductility and toughness of AISI 1020 steel are studied. Thick, hard, non-acicular and uniform boride layer are obtained as a result of laser boriding. The impact test results indicate that the laser borided specimens treated at higher energy densities of the laser beam have better ductility and toughness as compared with the specimens treated with lower energy densities of the laser beam as well as the continuous and the interrupted borided specimens.
关键词： Microstructure,Multicomponent boriding,Laser beam,Hardness gradient,Steel,Ductility and Toughness
更新于2025-09-12 10:27:22
-
Fracture Toughness of a Hot Work Tool Steel Fabricated by Laser‐Powder Bed Fusion Additive Manufacturing
摘要： The fracture toughness of AISI H13 tool steel, additively manufactured by laser powder bed fusion (L-PBF) technique was studied. The influence of the building direction on fracture toughness was investigated on small notched bending samples heat treated according to two different thermal cycles, namely quenching and tempering (QT) and only tempering (T). The notch was electro discharge machined parallel (P//), perpendicular (P┴) and longitudinal (L) to the building direction. Both heat treatments, even if to a different extent, delete the as-built microstructure, producing secondary carbides precipitation in the martensitic matrix. The microstructure of the directly tempered parts is finer than the quenched and tempered ones. The fracture toughness increases moving from P┴ to P//. The T samples show a higher apparent fracture toughness in the P//, despite the higher hardness. Secondary cracks formation allows toughness in P// samples. This effect is more pronounced in T samples where the stronger precipitation of carbides at the prior melt boundaries promotes secondary cracks. Moreover, in P// samples the laser tracks act as barriers to crack propagation and as stress dissipators.
关键词： Laser powder bed fusion,hot work tool steel,fracture toughness,microstructure
更新于2025-09-12 10:27:22
-
[Laser Institute of America ICALEO? 2016: 35th International Congress on Applications of Lasers & Electro-Optics - San Diego, California, USA (October 16–20, 2016)] International Congress on Applications of Lasers & Electro-Optics - Alteration of fracture toughness (KIC) following laser shock peening of silicon nitride ceramics
摘要： This work focuses on the development in laser shock peening (LSP) Si3N4 ceramics with a view to first observe the general effects namely; the topography, hardness, flaw size, plane strain fracture toughness (KIc). Firstly, an LSP surface treatment was conducted to establish a crack-free surface treatment. This also established a parametric window and elucidated the feasibility of treating a brittle material such as Si3N4 with a high intensity/pressure surface treatment such as LSP. Upon comparing the as-received surface with the LSPned surface elucidated a natural increase in surface roughness from an average of 1.73μm to 4.79μm. This indicated some level of material removal. In addition, a decrease in hardness was found by 4.5% and an increase in the KIc by over 21.5% through a possible induction of plasticity within the Si3N4. The microstructure of the Si3N4 also showed considerable changes after LSP surface treatment and a possible α-beta transformation were introduced which indicated surface strengthening. The work undertaken herein have shown that with further refinement of the LSP parameters, this type of laser treatment could be beneficial for strengthening advanced ceramics, particularly, as the process offers a mechanism for enhancement in fracture toughness. An alteration of such an important property of a Si3N4 would open new avenues for its applications particularly where metals and alloys fail.
关键词： hardness,surface treatment,Laser shock peening,Si3N4 ceramics,fracture toughness
更新于2025-09-11 14:15:04
-
Strength and toughness anisotropy in hexagonal boron nitride: An atomistic picture
摘要： Strength and toughness are two crucial mechanical properties of a solid that determine its ability to function reliably without undergoing failure in extreme conditions. While hexagonal boron nitride (hBN) is known to be elastically isotropic in the linear regime of mechanical deformation, its directional response to extreme mechanical loading remains less understood. Here, using a combination of density functional theory calculations and molecular dynamics simulations, we show that strength and crack nucleation toughness of pristine hBN are strongly anisotropic and chirality dependent. They vary nonlinearly with the chirality of the lattice under symmetry breaking deformation, and the anisotropic behavior is retained over a large temperature range with a decreasing trend at higher temperatures. An atomistic analysis reveals that bond deformation and associated distortion of electron density are nonuniform in the nonlinear regime of mechanical deformation, irrespective of the loading direction. This nonuniformity forms the physical basis for the observed anisotropy under static conditions, whereas reduction in nonuniformity and thermal softening reduce anisotropy at higher temperatures. The chirality-dependent anisotropic effects are well predicted by inverse cubic polynomials.
关键词： chirality,anisotropy,hexagonal boron nitride,molecular dynamics simulations,density functional theory,strength,toughness
更新于2025-09-10 09:29:36
-
Spark Plasma Sintering of Silicon Carbide with Al <sub/>2</sub> O <sub/>3</sub> and CaO: Densification Behavior, Phase Evolution and Mechanical Properties
摘要： Liquid phase sintering (LPS) often yield an amorphous grain boundary region which deteriorates the high temperature properties of the sintered ceramics and thus ceramists prefer to obtain a crystalline grain boundary after LPS. This paper deals with LPS of silicon carbide ceramics to near theoretical density, understanding the densification behavior, evolution of gehlenite phase and subsequent evaluation of their mechanical properties. High density SiC ceramics were fabricated from sub-micrometre α-SiC powders with the aid of refractory phase forming metal oxide additives by spark plasma sintering. Sintering temperature and holding time at peak temperature were varied to study their effect on densification and mechanical properties. Density of the sintered ceramics reached ~97% at 1800oC. Microstructural features and crack propagation mode were studied using scanning electron microscopy. XRD analysis confirmed the presence of crystalline gehlenite phase in the sintered samples. Hardness, fracture toughness and flexural strength of the sintered ceramics were determined by standard test procedures.
关键词： Liquid phase sintering,Fracture toughness,Spark plasma sintering,Silicon carbide,Mechanical properties
更新于2025-09-09 09:28:46
-
Heterogeneity governs diameter-dependent toughness and strength in SiC nanowires
摘要： Using a combination of density functional theory and molecular dynamics simulations, this paper reveals the atomistic origin of diameter-dependent extreme mechanical behavior of [111] 3C-SiC nanowires obtained from an energy-based framework. Our results suggest that heterogeneity in atomic stress and variations in diameter-dependent potential-energy density have a profound impact on extreme mechanical properties in the nanowires. The heterogeneity in stress evolves from the nonuniform bond lengths mediated by low coordinated surface atoms—and it penetrates the entire cross section in thinner nanowires and constitutes the atomistic basis for their large reduction in fracture strain, toughness, and strength. Although stress heterogeneity is substantially higher in ultrathin nanowires, its intensity drops and saturates rapidly in larger nanowires following a nonlinear dependence on diameter. The maximum stress heterogeneity in a cross section localizes crack nucleation at the core in ultrathin nanowires but near the surface in larger nanowires. Moreover results show that stiffness, toughness, strength, and fracture strain of the nanowires increase nonlinearly with increasing diameter and saturate at a lower value compared to bulk SiC. In addition to resolving wide discrepancies in the reported values of the ?rst-order elastic modulus in SiC nanowires, the ?ndings highlight heterogeneity as a critical factor for inducing diameter-dependent extreme mechanical behavior in brittle nanowires.
关键词： heterogeneity,atomic stress,strength,toughness,potential-energy density,fracture strain,SiC nanowires,diameter-dependent,mechanical properties
更新于2025-09-09 09:28:46