Papers by Keyword: In Situ Synthesis

Abstract: Niobium (Nb) and titanium (Ti) react with carbon to form high-melting-point and high-hardness MC-type carbides. This study explores the in-situ synthesis of mixed NbC-TiC carbides during plasma transferred arc welding of a steel-based hardfacing. Feedstock powders consisted of stainless steel AISI 316L, TiO₂, and graphite with and without 5 wt.% Nb addition. Feedstock powders were ball milled for 72 hours, then mixed with paraffine and pre-placed on the S235 steel. The cladding current was 125 A, and the plasma torch travel velocity was 1 mm/s and 0.7 mm/s. The effect of Nb on TiC generation was examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS). Vickers hardness was also measured at the surface of hardfacings. Results show that previously formed NbC grains acted as nucleation sites for TiC precipitation. Increased torch velocity has resulted in improving distribution and decreasing agglomeration of carbon phases. Hardness tests showed that Nb and Ti increased the hardness resistance of the substrate steel.

Abstract: This study aimed to compare the X3CrNiMo17-13-3 stainless steel based plasma transferred arc (PTA) cladded hardfacings, reinforced with the in-situ synthesized Cr and Ti carbides. Carbon black and either pure Cr, pure Ti, or TiO₂ were utilized as reinforcement precursors (the respective hardfacings are further referred to as Cr+C, Ti+C and TiO₂+C). The pre-placed mixtures of matrix and reinforcement precursor powders were remelted by the plasma transferred arc, applying the preliminarily optimized process parameters (95 A, 22 – 24 V, 0.2 mm/s). As a reference, the unreinforced stainless steel hardfacing was used. The carbide reinforcement was successfully in-situ synthesized in all the hardfacings. The Cr + C hardfacing exhibited the largest average hardness (556 ± 29 HV1), while the TiO₂ + C hardfacing had the largest average Young’s modulus (156.3 ± 19.7 GPa). The Cr + C and Ti + C hardfacings demonstrated the 2.3 and 2.1 times higher resistance to abrasive wear than the reference hardfacing. The TiO₂ + C hardfacing showed 1.5 times lower wear resistance than the reference hardfacing presumably due to a lack of the reinforcement and a lower strain hardening ability.

Abstract: This paper presents the results of the study of Selective Laser Melting (SLM) process for the in-situ synthesis of Ti-6Al-4V alloy from elemental powder mixture. Elemental spherical powders of Ti, Al and V were used to prepare a powder mixture, and then bulk specimens were produced by SLM using different process parameters. The effects of SLM process parameters on samples’ relative density, their chemical composition, the formed microstructure and microhardness before and after heat treatment have been studied. It was shown that volume energy density during the SLM process significantly effects the microstructure and microhardness of Ti-6Al-4V obtained from elemental powders. The difference in microstructure morphology and microhardness remains after heat treatment.

Abstract: In this paper, the metal/ceramic functionally graded composites are prepared. The thermal stress of TiC/Ti functionally graded composites are simulated by Abaqus finite element analysis software to study the influence of the number of layers, the gradient layer thickness and the gradient of distribution index.The optimal structural parameters of the TiC/Ti functional gradient composites are obtained as the number of layers of 6 and the gradient distribution index 0.8. According to the optimized structural parameters, Ti and C powders are mixed by high-energy ball milling, then the TiC/Ti functional gradient composites are prepared by spark plasma sintering. The gradient distribution of composition and microstructure in TiC/Ti functionally graded composites are achieved, which can solve the problem of mismatch for the physical properties between the metal and the ceramic in the composite material.

Abstract: In this work, monodispersed silver nanoparticles with controllable size have been successfully in situ synthesized in PMMA matrix. NaHS, HCl and poly (vinyl pyrrolidone) (PVP) were used to optimize the nucleation and growth of silver nanocrystalline. UV–vis analysis and transmission electron microscopy (TEM) were used to characterize the size and dispersion of silver nanoparticles in the Ag/PMMA nanocomposites. The results show that silver nanoparticles homogeneously distribute in PMMA/DMF sol and the particle size of silver nanoparticles increase with the increasing of time. The nucleation of Ag atoms can be facilitated through the addition of a trace amount of NaHS to generate Ag₂S clusters as heterogeneous nuclei. Introducing a trace amount of Cl^- into the reaction system can effectively reduce the growth rate of the nanoparticles and thus generating more uniform silver nanoparticles in PMMA matrix.

Abstract: In this paper, In Situ AlN particles reinforced magnesium matrix composites were fabricated. The results show that the AlN phases can be In Situ synthesized in AZ91D alloy with the addition of Mg₃N₂. The microstructure and phases of the matrix alloys and the composites were investigated by OM, SEM and XRD. The hardness and mechanical properties of the matrix alloys and the composites were also obtained. Compared with those of the matrix alloy, the grains of composites were refined obviously and the mechanical properties of composites were improved significantly. The microstructural analysis indicates that the AlN particles can act as the heterogeneous nucleation of α-Mg phases in the composites. The strengthening mechanism of the composites with AlN particles was discussed.

Abstract: This article uses the cast-penetrated-heat treatment process produce V₈C₇ particle on the surface of iron base composite material, and analyze its organizing appearance using methods such as XRD, SEM, measured its hardness with micro hardness tester of type TUKON2100, operate wear test under different load with wear test machine of ML-100. Results show that the surface of the particle reinforced iron matrix V₈C₇ composite sample maximum microhardness is 2333 HV_0.05. At room temperature, when the load is 15N, its average abrasive resistance is about 13 times that of it of grey cast iron, which improves the wear resistance of the iron substrate to a great extent.

Abstract: Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases has focused considerable attention in recent decades because significant improvement in mechanical properties and thermal stability. This paper has considered in-situ fabrication by mean of reactive sintering of blended and compacted powders containing an aluminum-copper hardenable alloy and titanium dioxide. An experimental program has been dedicated to optimize the sintering parameters in terms of both treatments temperature, between 650 and 800°C, and duration, in the range of 3 to 6 hours. Microstructural analysis based on Scanning Electron Microscopy (SEM) has been used to determine of distribution of elements involved in sintering reactions, such as aluminum, titanium and oxygen.

Abstract: The hydrophobic gold nanoparticles with monodispersity are synthesized by using n-butanol reduction in situ under the condition of alkali promotion in cetyltrimethylammonium bromide (CTAB)/n-butanol/n-heptane/HAuCl₄/NaOH(aq) W/O microemulsion at 30°C. The CTAB-stabilized gold nanoparticles are characterized by UV-vis, TEM , XRD and so on. The replacement of simple surfactant (CTAB ) with mixed surfactant CTAB/ octadecylamine can weaken the direction of CTAB to the growth of gold nanopartices and increase the monodispersity of gold nanoparticles. The effects of components of the microemulsion system on the shape, size and monodispersity of gold nanoparticles are also explored. The results show that the size of gold particles is changed by the amount of CTAB and C₁₈NH₂.

Abstract: The in situ synthesized ZrC particulate reinforced metal matrix composite coating was fabricated on AISI1020 steel by gas tungsten arc (GTA) cladding powder mixture of Nickel, Zirconium and Graphite. The microstructure and wear resistance of the composite coating were investigated. It is shown that the coating is bonded metallurgically to the substrate and has a homogeneous fine microstructure containing both approximate cubic ZrC particle uniformly dispersed in matrix of (Fe,Ni) solid solution. Compared to a substruate, the hardness of the composite coating was increased by a factor of 6, could achieve a Vicker microhardness of HV_0.21100. And the wear resistance in a block on ring test against YG8 was increased by a factor of 10. This is attributed to the presence of in situ synthesized ZrC particles and their well distribution in the coating.