- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Microstructural characterization of nanostructured Al2O3-ZrO2 eutectic layer by laser rapid solidification method
摘要： In the present work, nanostructured surface layers of Al2O3-ZrO2 eutectic with a thickness of approximate 1000 μm and free of cracks and pores were produced on the surface of conventionally-sintered Al2O3-ZrO2 ceramic via the laser irradiation rapid solidification process. The molten pool geometry and microstructure were characterized by scanning electron microscopy and Raman spectroscopy. The geometrical evolution of molten pool in response to laser power and laser scanning velocity was established, where the top view of molten pool exhibits a circular shape at low velocities and gradually evolves into an oval-shaped surface at high velocities. Singular Al2O3-ZrO2 eutectic colonies with a size of 100-200 μm, which is formed around a spontaneously nucleated dendritic ZrO2 core, are found on the surface of laser-remelted layer. The eutectic colony has an interphase spacing of 190-280 nm. The variation of eutectic spacing with growth rate is essentially linear on the logarithmic scale as λ=KV-0.4 by binary regression analysis. Predicted by the Jackson-Hunt theory on eutectic solidification (JH theory), the eutectic spacing is consistent with the inverse-square-root dependence on growth rate with a proportionality constant of 3.32. The eutectic colonies consist of α-Al2O3, t-ZrO2 and m-ZrO2 phases, where α-Al2O3 and t-ZrO2 are the dominant phases and the m-ZrO2 phase increases with the decrease of laser scanning velocity.
关键词： Al2O3-ZrO2,Nanoeutectic layer,Laser remelting,Surface nanostructuring
更新于2025-11-28 14:24:20
-
Scratch resistance and damage mechanism of laser remelted thermally sprayed ceramic coating
摘要： Scratch resistance of plasma sprayed and laser remelted alumina and chromia coatings were assessed under constant and variable load. Failure load and cohesive strength of the coatings increased up to 65% and 94%, respectively upon laser remelting. The scratch wear resistance increased up to 88%. This is attributed to an improvement in hardness, elastic modulus and indentation fracture toughness of the remelted coatings. Upon laser remelting, lamellar microstructure of thermally sprayed coating was transformed into a columnar microstructure. A phase change from γ-alumina to α-alumina also occurred. Principal mechanisms of failure of the coatings were plastic deformation, tensile cracking, and spallation. In both types of coatings, a subsurface crack was found to grow in a direction parallel to the scratch. Propagation of this crack to the surface produced spallation of the coating. In the ball on disc test, the coatings were found to fail by splat delamination and radial cracking. The wear coefficients of the laser remelted chromia and alumina coating, respectively were 80% and 72% lower than those of the as-sprayed coatings.
关键词： radial crack,splat delamination,laser remelting,chromia,scratch wear
更新于2025-11-21 11:18:25
-
Effect of Static Magnetic Field on the Evolution of Residual Stress and Microstructure of Laser Remelted Inconel 718 Superalloy
摘要： As a typical additive manufacturing technique, direct energy deposition is restricted from further application due to the presence of residual stress and the structural deformation. Thus, minimizing the residual stress plays a crucial role in additive manufacturing. In this work, a transverse static magnetic field is introduced in the laser remelting of Inconel 718 superalloy to investigate the effects on residual stress and microstructural change. The x-ray diffraction technique was used to examine the residual stress variation. Optical microscope and scanning electron microscope were applied to observe the microstructure evolution. It was found that the compressive residual stress of the remelted region was notably reduced from 392.50 to 315.45 MPa under the effect of the magnetic field of 0.55 T. Furthermore, it was observed that the average dendrite spacing was reduced by about 32% under the magnetic field. During the laser remelting process, the imposed electromagnetic force minimized the flow field within the molten pool, inhibiting the heat transfer and minimizing the cooling rate. These directly reduced the residual stresses. Based on research findings, the magnetic field can be a potential method to eliminate the residual stress in laser additive manufacturing components.
关键词： laser direct deposition,static magnetic field,Inconel 718 superalloy,laser remelting,residual stress,thermoelectric magnetic force
更新于2025-09-23 15:21:01
-
Selective Laser Melting and Remelting of Pure Tungsten
摘要： The processing of pure tungsten encounters a substantial challenge due to its high melting point and intrinsic brittleness. Selective laser melting (SLM) technique is gaining popularity and offers an excellent processing approach for refractory metals. Herein, dense pure tungsten specimens are produced by optimizing SLM processing parameters. The mechanical property of the SLM-produced tungsten with an ultimate compressive strength of about 1200 MPa, which is obviously superior to that reported in other literature, is achieved. The increased laser energy input is instrumental in raising density and surface roughness of tungsten specimens. Interestingly, additional remelting of processed layers during SLM improves the surface quality and the microstructure and achieves the highest relative density (98.4% (cid:1) 0.5%). After laser remelting, the surface roughness is reduced by 28% and a large number of ?ne grains are obtained. The ?ow of ?uids caused by remelting plays a decisive role in the formation of ?ne grains and the defect level. Therefore, these ?ndings offer a new insight into SLM of pure tungsten.
关键词： microstructure,tungsten,selective laser melting,mechanical properties,laser remelting
更新于2025-09-23 15:19:57
-
The roles of stress in the thermal shock failure of YSZ TBCs before and after laser remelting
摘要： In order to reveal the roles of stress in the thermal shock failure of thermal barrier coatings (TBCs), yttria-stabilised zirconia (YSZ) TBCs were prepared via atmospheric plasma spraying and then remelted by a laser remelting process. Subsequently, thermal cycling tests of the as-sprayed YSZ TBCs and remelted YSZ TBCs were carried out at 1100 °C. The thermal shock failure mechanism of the two TBCs was investigated comparatively from the perspective of stress, i.e., phase transformation stress of ceramic coating, growth stress and thermal mismatch stress generated by thermally grown oxide (TGO). The results showed that, compared with the as-sprayed YSZ TBCs, there was no m-ZrO2 in the remelted YSZ TBCs, which avoided the ceramic coating phase transformation stress produced by the transformation between m-ZrO2 and t-ZrO2 during thermal cycling. Therefore, the thermal shock failure mode of the as-sprayed YSZ TBCs was severe buckling driving delamination, while that of the remelted YSZ TBCs was slight edge delamination. In addition, the TGO growth stress and the thermal mismatch stress between the TGO and the bonding coating were reduced by the laser remelting treatment, leading to the spallation tendency of YSZ TBCs was decreased. Consequently, the remelted YSZ TBCs exhibited superior thermal shock resistance to the as-sprayed YSZ TBCs. Therefore, the phase transformation stress, growth stress and thermal mismatch stress determined the thermal shock failure mode and thermal shock life of these two YSZ TBCs.
关键词： Stress,Laser remelting,TGO,Thermal shock failure mechanism,TBCs
更新于2025-09-23 15:19:57
-
Bionic Repair of Thermal Fatigue Cracks in Ductile Iron by Laser Melting with Different Laser Parameters
摘要： Nodular iron brake discs typically fail due to serious thermal fatigue cracking, and the presence of graphite complicates the repair of crack defects in ductile iron. This study presents a novel method for remanufacturing ductile iron brake discs based on coupled bionics to repair thermal fatigue cracks discontinuously using bio-inspired crack blocking units fabricated by laser remelting at various laser energy inputs. Then, the ultimate tensile force and thermal fatigue crack resistance of the obtained units were tested. The microhardness, microstructure, and phases of the units were characterized using a digital microhardness meter, optical microscopy, scanning electron microscopy, and X-ray di?raction. It was found that the units without defects positively impacted both the thermal fatigue resistance and tensile strength. The unit fabricated at a laser energy of 165.6+19?15 J/mm2 had su?cient depth to fully close the crack, and exhibited superior anti-cracking and tensile properties. When the unit distance is 3 mm, the sample has excellent thermal fatigue resistance. In addition, the anti-crack mechanism of the units was analysed.
关键词： bionic crack blocked unit,repair discontinuously,thermal fatigue crack,ductile iron,laser remelting
更新于2025-09-23 15:19:57
-
The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations
摘要： Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value was characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.
关键词： microhardness,laser remelting,temperature distribution,laser boriding,cooling rate,microstructure
更新于2025-09-19 17:13:59
-
Microstructure and selected properties of boronized layers produced on C45 and CT90 steels after modification by diode laser
摘要： The paper presents the study results of macro- and microstructure, microhardness and corrosion resistance of C45 medium carbon steel and CT90 high carbon steel after diffusion boriding and laser modification by diode laser. It was found that the increase of carbon content reduced the thickness of boronized layer and caused change in their morphology. Diffusion boronized layers were composed of FeB and Fe2B iron borides. As a result of laser surface modification of these layers, the microstructure composed of three areas: remelted zone, heat affected zone (HAZ) and the substrate was obtained. Microhardness of laser remelting boronized layer in comparison with diffusion boronized layer was lower. The presence of HAZ was advantageous, because mild microhardness gradient between the layer and the substrate was assured. The specimens with laser boronized layers were characterized by better corrosion resistance than specimens without modified layer.
关键词： Laser remelting,Boronized layer,Corrosion resistance,Microstructure,Microhardness
更新于2025-09-16 10:30:52
-
Thermal Shock Resistance of Thermal Barrier Coatings with Different Surface Shapes Modified by Laser Remelting
摘要： Inspired by the unique structures and shapes of biological organisms, thermal barrier coatings (TBCs) with different shapes including dot, striation and grid were modified by laser remelting. NiCrAlY/ZrO2-7 wt.%Y2O3 double-layer-structured TBCs were prepared. The microstructure, microhardness, phase composition and thermal shock behaviors of the as-sprayed and laser-treated specimens with different shapes were examined. The results indicated that the unit was characterized by the dense columnar crystal structure and the high microhardness. The thermal cycle lifetime of the dotted specimen was about twice that of the as-sprayed specimen. On the one hand, due to the elimination of defects and higher hardness after laser remelting, the dotted unit could resist thermal crack propagation. On the other hand, the columnar grains and segmented cracks in the dotted units were beneficial to increase the strain tolerance. However, due to more continuous segmented cracks and transverse cracks, the striated and grid specimens had relatively poor thermal shock resistance.
关键词： laser remelting,thermal barrier coatings,thermal shock resistance,surface shape
更新于2025-09-04 15:30:14