Papers by Author: Jian Jiang Wang

Abstract: This paper shows a new type of manual SHS welding rod for normal carbon steel, called the pulse combustion rod. The structure and constitution of the pulse combustion rod was designed after the analysis of the problems and insufficiency of the normal manual SHS welding rod (normal combustion rod for short) in the vertical welding. Then the low carbon steel as the base metal was used for vertical weld experiment. Analysis of SEM, XRD and EDS shows that weld seam is composite of Fe-riched phase and Cu-riched phase, with much α-Fe but a little FeNi, ε-Cu and Cu_0.81Ni_0.19 contained in Fe-riched phase, and with much ε-Cu but a little Cu_0.81Ni_0.19, α-Fe and FeNi contained in Cu-riched phase. The interfacial adhesion between Cu-rich phase and Fe-rich phase is effectively improved for the Ni content in two phases is roughly the same. The weld seam alloy has a good bond with the base metal. The mechanical properties test of weld joint present that tensile strength is up to 367MPa and the hardness of weld alloying zone is HV143.8.

Abstract: The temperature change process of the single sprayed composite powder during the self-reactive spray forming process for preparing the Ti (C,N)-TiB₂ ceramic preforms was numerically simulated by means of finite element analysis. The results show that after the sprayed composite powder with grain size of 50μm has entered the flame field for 0.35ms, the surface temperature of it will reach the igniting temperature and the self-propagating high-temperature synthesis (abbr. SHS) reaction will take place. The heating rate of the particle in this period is about 2.82×10⁶°C/s. After the SHS reaction has taken place, the heating rate becomes quicker because of the double function of the flame and the reactive heat release. When the temperature of the sprayed particle is higher than that of the flame, the heat exchange process will turn into heat absorption from heat release, which leads to the great drop of the heating rate (about 1.20×10⁶°C/s). The composite powder completes the reaction in 0.88ms and reaches the highest temperature of 2920°C, which makes it become a ceramic droplet. After the reaction has finished, the droplet cools down quickly from exterior to interior, and the surface temperature of it descends to the theoretic eutectic melting point of the composite ceramics (2620°C) after 0.34ms. Then the droplet begins to solidify at some degree of supercooling and becomes ceramic particle. The numerically simulated results before, during and after the reaction match the water-quenching experiments of the sprayed particle with particle size of 50μm during the corresponding period. It indicates the heat process of the sprayed composite powder on the whole, which is composed of being heated, heat releasing, cooling and solidifying.

Abstract: In order to improve microwave absorption properties of hollow ceramic microspheres (HCMs) and possess the better characteristics of “thinness、width、lightness、strongness”, used Al+Cr₂O₃ as the main reaction system, hollow ceramic microspheres were prepared by SHS flame quenching technology. Microwave absorption properties of HCMs were studied when the additive is Fe. The results show that microwave absorption properties of HCMs depend on the dielectric property of product, such as SiC、mullite, when there is no additive. However, when Fe is used as additive, the microwave absorption properties of HCMs are better. SHS reaction of agglomerate powders is happened in the flame field and SiC、Fe₂O₃、Al₃Fe₅O₁₂、Cr_1.3Fe_0.7O₃、(Fe_0.6Cr_0.4)₂O₃ are synthesized. Except the dielectric property of SiC, magnetic property of HCMs is possessed due to the ferruginous materials are synthesized. So its microwave absorption properties are stronger. Keywords: additive; hollow ceramic microspheres; microwave absorption properties

Abstract: The multiphase coatings with major phases Al2O3-AlxCuy were prepared by the reactive flame spray technology. The melting and reactive behavior of the Al-CuO agglomerated particles and the forming process of the coatings were studied by means of water-quenching experiments and the methods of XRD and SEM. It was shown that during the spray distance between 60 and 150 millimeters, CuO in the agglomerated particles was heated to decompose into Cu2O, Cu and O2. During the flying course, a little of Al reacted with Cu2O and produced Al2O3 and Cu. The reduced Cu mutually dissolved with Al and formed liquid Al-Cu alloy. After the spray particles bumped into the substrate, Cu2O reacted with Al richly, then lots of Al2O3 was produced and Cu was reduced at the same time. These products were wallowed up by the liquid Al-Cu alloy soon. When the temperature of the system dropped quickly, the structure transforming process began. The intermetallics of Cu9Al4 and Al2Cu3 were deposited from the liquid Al-Cu alloy via complicated eutectic reaction and eutectoid reaction.

Abstract: The preparation, mechanism and electromagnetic absorbing properties of Hollow Ceramic Micro-spheres (HCMs) were studied in the present investigation. HCMs were produced by traditional flame spraying technology as well as equipments. Al-TiO₂ was chosen as a main reactive system. The self-reactive agglomerate powders were produced by spraying process by adopting a temperature-controlled media to get the high cooling rate to solidify and crystallize rapidly. HCMs with characteristic of hollow structure and in-situ synthesis were obtained. Electromagnetic parameter of HCMs has been tested and the reflectivity was analyzed. The results showed that HCMs possess the microwave absorbing properties. The relationship between intrinsic parameters of HCMs and microwave absorbing properties has been also investigated.

Abstract: Numerical simulation the temperature and stress of the SHS reactive flame spray coatings which were cooled in air and sand from a high temperature to room temperature (25°C). The distribution of temperature and stress of the coatings were discussed. The results show that the cooling velocity of air-cooled product is fast than that of sand-cooled product; temperature distribution of sand-cooled product is more uniform than that of air-cooled product in the process of cooling; the stress state of air-cooled coating is tensile stress state, while the stress state of sand-cooled coating is compressive stress state; the stress distribution and strain situation are close relative to temperature distribution, heat emission speed and geometric shape of products in process of cooling; the smooth geometric shape of the product, uniform temperature distribution and heat emission speed are beneficial to improve the state of residual thermal stress; the stress and strain state of sand-cooled coating is better than that of air-cooled coating.

Abstract: Based on the Ti-B4C-sucrose(precursor of carbon) -5wt.% Al sprayed system, the self-reactive spray formed multi-phased structural ceramic preforms tests were done. And the organization, structure and performances of the products were studied. The results show that the products are composed of continuous matrix phase TiC0.3N0.7, dispersed micro/nanometric rodlike grains TiB2, some of Al2O3, pores and intermetallic phase Ti3Al which is hard to identify by SEM. Aluminum is benefit to improve organization, structure and performances of the products. The average density of the products is 97.7%, the Vickers hardness is 20.6GPa, and the flexural strength is 425MPa. There are crack deflection and grain bridging toughening mechanisms owing to the rodlike grains of TiB2 in the products, which makes their fracture toughness is as high as 7.3MPa•m1/2.

Abstract: With Ti-B4C-C as self-reactive spray forming system, the flying combustion process of the sprayed particles was studied by means of water-quenching experiments and numerical simulation. It was found that after the particles have been heated in the oxyacetylene flame for a short time, Ti in the particles melts first and then infiltrates B4C and C. The SHS reaction of the sprayed particles takes place subsequently. Then the liquid ceramic beads appear and crystallize into ceramic grains finally. By the ANSYS finite element analysis, it can be known that the SHS reaction of the sprayed particles starts after they have left the muzzle for about 9.5×10-4s and lasts about 1.45×10-3s before the ceramic beads solidify. The calculated optimal melting distance for the spray particles is about 116mm, which is consistent with the experimental results on the whole.

Abstract: Al2O3-TiO-TiO2 multiphase foam ceramic was prepared with Al powders and TiO2 powders by combustion synthesis, Direct observation and metallographic microscope indicated that the pore diameter is 100~6000μm, and Archimedean method showed that the porosity is 35~50%. The influencing factors of the pore diameter and porosity and, the effects of adding SiO2 on compression strength of the Al2O3- TiO-TiO2 multiphase foam ceramic were discussed. It was shown that the addition of proper high temperature foaming agent can increase porosity and adding SiO2 can decrease porosity. The Al2O3-TiO-TiO2 multiphase foam ceramic has good mechanical properties and high-temperature resistance.

Abstract: A new near-net-shape technology, namely, self-reactive spray forming, to prepare ceramic preforms with low cost was proposed by combining the self-propagating high-temperature synthesis (SHS) with the metal spray forming. The feasibility of the technology was illustrated. And TiC-TiB2 -based structural ceramic was prepared by the new technology. The microstructure of the self-reactive spray formed preforms was analyzed. It was shown that the self-reactive spray formed preforms are composed of four kinds of structure, which takes on the characteristics of rapid solidification. They are griseous continuous base phase TiC0.3N0.7, black columnar grain TiB2 with the size of 100nm-1μm, white by-product phase TiO2 distributing along the boundary of the base phase, and a few of black anomalous pores respectively.