叠层陶瓷喷嘴的冲蚀磨损@中英文翻译@外文翻译

ZhaoevaluateduringC211 2006 Elsevier Ltd. All rights reserved.abrasive particles and carrier gas coming out from a nozzleimpinges on the target surface and erodes it. The fine par-mass flow rate and impact angle 57, the erodent abrasiveproperties 810, the nozzle material and its geometrysection in sand blasting (see Fig. 1), the nozzle entry regionsuers form severe abrasive impact, which may cause largetance 1922. Residual stresses arise from a mismatchbetween the coecients of thermal expansion (CTE), sin-tering rates and elastic constants of the constituent phasesand neighbouring layers, and the residual stress fielddepends on the geometry of the layered structure and onthe thickness ratio among layers 2326. Toschi 22*Corresponding author. Tel.: +86 531 88392047.E-mail address: (D. Jianxin).International Journal of Refractory Metals & Hardticles are accelerated by the gas stream, commonly com-pressed air at a few times atmospheric pressure. Theparticles are directed towards the surfaces to be treated.As the particles impact the surface, they cause a small frac-ture, and the gas stream carries both the abrasive particlesand the fractured particles away. The nozzle is the mostcritical part in the sand blasting equipment. There aremany factors that influence the nozzle wear such as: thetensile stresses. The highest tensile stresses are located atthe entry region of the nozzle. Thus, the erosion wear ofthe nozzle entry region is always serious in contrast withthat of the center area 11,15.Laminated hybrid structures constituted by alternatelayers of dierent materials can be properly designed toinduce a surface compressive residual stress leading to animproved surface mechanical properties and wear resis-Keywords: Nozzles; Ceramic materials; Laminated materials; SiC1. IntroductionSand blasting treatment is an abrasive machining pro-cess and is widely used for surface strengthening 1, surfacemodification 2, surface clearing and rust removal 3,4,etc. It is suitable for the treatment of hard and brittle mate-rials, ductile metals, alloys, and nonmetallic materials. Inthe sand blasting process, a very high velocity jet of fine1116, and the temperatures 17,18. Ceramics, beinghighly wear resistance, have great potential as the sandblasting nozzle materials.Several studies 11,15 have shown that the entry area ofa ceramic nozzle exhibited a brittle fracture inducedremoval process, while the center area showed plowingtype of material removal mode. As the erosive particleshit the nozzle at high angles (nearly 90C176) at the nozzle entryErosion wear of laminatedDeng Jianxin*, Liu Lili,Department of Mechanical Engineering, Shandong UniversitReceived 31 March 2006;AbstractSiC/(W,Ti)C ceramic nozzles with laminated structures were producedand exit region of the nozzle. Finite element method was used tocoecients and shrinkage of the SiC and (W,Ti)C solidsolutionthe laminated ceramic nozzle was assessed by sand blasting; the resultsnozzle with the same composition. The experimental results have shownresistance to that of the homologous stress-free nozzles.0263-4368/$ - see front matter C211 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.ijrmhm.2006.06.005ceramic nozzlesJinlong, Sun Junlongy, Jinan 250061, Shandong Province, PR Chinaaccepted 30 June 2006by hot pressing in order to reduce the tensile stress at the entrythe residual stresses due to the dierent thermal expansionthe sintering process of the composite. The erosion wear ofwere compared with those obtained with an unstressed referencethat the laminated ceramic nozzles have superior erosion /locate/ijrmhmMaterials 25 (2007) 263270element method. The erosion wear ofthe laminatedceramicnozzles was investigated in comparison with an unstressedreference nozzle with the same composition.2. Materials and experimental procedures2.1. Preparation of SiC/(W,Ti)C laminated ceramicnozzle materialsThe starting materials were (W,Ti)C solidsolution pow-ders with average grain size of approximately 0.8 lm, pur-ity 99.9%, and SiC powders with average grain size of1 lm, purity 99.8%. Six dierent volume fractions of(W,Ti)C (55, 57, 59, 61, 63, 65 vol.%) were selected indesigning the SiC/(W,Ti)C laminated nozzle material witha six-layer structure. The compositional distribution of thelaminated ceramic nozzle materials is shown in Fig. 2.Itisindicated that the compositional distribution of the lami-264 D. Jianxin et al. / International Journal of Refractory Metals & Hard Materials 25 (2007) 263270et al. reported that laminated hybrid structures canimprove the sliding wear resistance of alumina. Portu 27et al. showed that laminated structures with compressiveresidual stresses within the surface regions was a suitableway to obtain composite materials with superior tribologi-cal properties. Deng et al 28. showed that gradient cera-mic nozzle exhibited high wear resistance over commonceramic nozzles.In the present study, SiC/(W,Ti)C ceramic nozzles withFig. 1. Schematic diagram of the interaction between the erodent particleand the nozzle in sand blasting processes.laminatedstructureswereproducedbyhotpressinginorderto reduce the tensile stress at the entry and exit region of thenozzle. The residual stress of the laminated nozzle duringthe sintering process was calculated by means of the finiteFig. 2. Compositional distribution of (a) the SiC/(W,Ti)C ceramic nozzle laminatednozzles (CN-2).nated nozzle materials changes in nozzle axial direction.As the heat conductivity of SiC is higher than that of(W,Ti)C solidsolution, while its thermal expansion coe-cient is lower than that of (W,Ti)C, the layer with the high-est volume fraction of SiC was put both in the entry layerand in the exit layer (see Fig. 2(a). The homologous stress-free nozzle with no compositional change is shown in Fig. 2(b). The ceramic nozzle laminated both in entry and exitarea is named GN-3, while the stress-free nozzle is namedCN-2.Six SiC/(W,Ti)C composite powders of dierentmixture ratios were prepared by wet ball milling in alco-hol with cemented carbide balls for 80 h respectively.Following drying, the mixtures composite powders withdierent mixture ratios were laminated into the mouldin turn. The sample was then hot-pressed in flowingnitrogen for 40 min at 1900 C176C temperature with30 MPa pressure.both in entry and exit area (GN-3), (b) the homologous stress-free2.2. Sand blasting testsFig. 3 shows the schematic diagram of the abrasive air-catcher, an abrasive hopper, and a nozzle. The air and gritflow adjusting was controlled by the valves and regulators.The gas flow rate is controlled by the compressed air, andthe abrasive particle velocity through the nozzle is adjustedto 60 m/s.The erodent abrasives used in this study were of siliconcarbide (SiC) powders with 50150 lm grain size. TheFig. 3. Schematic diagram of the sand blasting machine tool (1) aircompressor, (2) control valve, (3) filter, (4) desiccator, (5) press adjustingvalve, (6) dust catcher, (7) blasting gun, (8) abrasive hopper, (9) ceramicnozzle).Fig. 5. Photo of the GN-3 laminated ceramic nozzles.D. Jianxin et al. / International Journal of Refractory Metals & Hard Materials 25 (2007) 263270 265jet machine tool (GS-6 type), which consists of an air com-pressor, a blasting gun, a control valve, a particle supplytube, a filter, a desiccator, an adjusting press valve, a dustFig. 4. SEM micrograph of the SiC abrasives used for sand blasting.SEM micrograph of the SiC powders used for the dry sandblasting is shown in Fig. 4.Nozzles with internal diameter 8 mm and length 30 mmmade from SiC/(W,Ti)C laminated structure (GN-3) andstress-free structure (CN-2) were manufactured by hot-pressing as can be seen in Fig. 5.The mass loss of the worn nozzles was measured with anaccurate electronic balance (minimum 0.1 mg). All the testconditions are listed in Table 1. The erosion rates (W)ofthe nozzles are defined as the nozzle mass loss (m1) dividedby the nozzle density (d) times the mass of the erodentabrasive particles (m2):Table 1Sand blasting test conditionsSand blasting equipment GS-6 type sand blasting machine toolNozzle material GN-3 laminated nozzle CN-2stress-free nozzleDimension of nozzle U8 mm (internal diameter) 30 mm (length)Erodent abrasives 50150 lm SiC powdersCompressed air pressure 0.4 MPaCumulative mass weigh Accurate electronic balance(minimum 0.1 mg)Table 2Hardness of dierent layers of the laminated nozzle materialsLayer (W,Ti)C content (vol.%) Vickers hardness Hv (GPa)1 55 26.892 57 26.523 59 25.934 61 25.705 63 24.676 65 24.15266 D. Jianxin et al. / International Journal of RefractoryW m1=d:m21where the W has the units of volume loss per unit mass(mm3/g).The finite element method (FEM) was used as a meansof numerically evaluating the residual stress and its distri-Fig. 6. SEM micrographs of each polished layer of the GN-3 laminated ceramicthird layer, (d) the fourth layer, (e) the fifth second layer, and (f) the sixth layer.Fig. 7. Distribution of (a) the axial (rz), (b) the radial (rr), and (c) the circumferenprocess.Metals & Hard Materials 25 (2007) 263270bution of the laminated ceramic nozzle in the fabricatingprocesses.For observation of the micro-damage and determinationof erosion mechanisms, the worn nozzles were sectionedaxially. The eroded bore surfaces of the nozzles were exam-ined by scanning electron microscopy.nozzle material (a) the first layer (entry zone), (b) the second layer, (c) thetial (rh) residual stresses in the GN-3 laminated nozzle in fabricatingD. Jianxin et al. / International Journal of Refractory3. Results and discussion3.1. Microstructural characterization and propertiesof the laminated nozzle materialsHardness measurements were performed by placingVickers indentations on every layer of the cross-sectionalsurface of GN-3 laminated nozzle material. The indenta-tion load was 200 N and a minimum of three indentationswere tested for each layer. The Vickers hardness (GPa) ofeach layer is given byHv 1:8544P2a22where P is the indentation load (N), 2a is the catercornerlength (lm) due to indentation. Hardness of each layerof the GN-3 laminated nozzle material is presented inTable 2.SEM micrographs of each polished layer of GN-3 lami-nated ceramic nozzle material are shown in Fig. 6. Theblack areas were identified by EDX analysis as SiC, andFig. 8. (a) The axial (rz), (b) the radial (rr), and (c) the circumferential (rh) residualposition along the axial direction of the nozzle.Metals & Hard Materials 25 (2007) 263270 267the white phases with clear contrast were (W,Ti)C. It canbeseenthattheSiCparticlesarequiteuniformlydistributedthroughout the microstructure, porosity is virtually absent.3.2. Residual stress at the laminated nozzlesThe residual stress of the laminated ceramic nozzle in thefabricatingprocesswascalculatedbymeansofthefiniteele-ment method by assuming that the compact is cooled fromsintering temperature 1900 C176C to room temperature 20 C176C.Thermo-mechanical properties of (W,Ti)C and SiC are asfollows:W;TiC : E 480 GPa; m 0:25; a 8:5C210C06KC01;k 21:4W=mK:SiC : E 450 GPa; m 0:16; a 4:6C210C06KC01;k 33:5W=mK:Owing to the symmetry, an axisymmetric calculationwas preferred. Presume that it was steady state boundaryconditions. The results of the distribution of the axialstresses in the GN-3 laminated nozzle in fabricating process at dierentshowed higher cumulative mass loss under the same testconditions.The worn ceramic nozzles were cut after operation inlongitudinal directions for failure analysis. Fig. 10 showsthe photos of the inner bore profile of the GN-3 andCN-2 nozzles after 540 min operation. It is showed thatinner bore diameter of the worn CN-2 nozzle along thenozzle longitudinal directions is larger than that of theworn GN-3 laminated nozzles, especially at the nozzleentry region.The results of the nozzle entry bore diameter variationwith the erosion time of for GN-3 and CN-2 nozzles areshown in Fig. 11. It is indicated that the entry bore dia-meter enlarges greatly with the operation time for CN-2stress-free nozzle. While the entry bore diameter increasesslowly with the operation time for GN-3 laminated nozzle.Fig. 12 shows the comparison of the erosion rates for GN-3and CN-2 nozzles in sand blasting processes. It is obviousthat the erosion rate of the stress-free nozzles is higherthan that of the laminated nozzles. Therefore, it is appar-ently that the GN-3 laminated nozzles exhibited higher ero-sion wear resistance over the CN-2 stress-free nozzle underthe same test conditions.268 D. Jianxin et al. / International Journal of Refractory Metals & Hard Materials 25 (2007) 263270(rz), the radial (rr), and the circumferential (rh) residualstresses calculated by FEM in the GN-3 laminated nozzlein cooling process from sintering temperature to room tem-perature are showed in Fig. 7. It is obvious that an excesscompressive residual stress is formed both at the entry andthe exit region of the GN-3 laminated nozzle. Fig. 8 showsthe axial (rz), the radial (rr), and the circumferential (rh)residual stresses in GN-3 laminated nozzle at dierent posi-tion along its axes. It in indicated that rz, rr, and rhresid-ual stress both at the entry zone and at the exit zone iscompressive, and the maximum value is C094.003 MPa,C0130.949 MPa, and C0265.368 MPa respectively. There-fore, laminated structures in ceramic nozzles can form anexcess compressive residual stresses at the entry and exitregion of the nozzle during fabricating process.3.3. Erosion wear of the laminated nozzleFig. 9. Cumulative mass loss of the GN-3 laminated nozzle and the CN-2stress-free nozzle in sand blasting processes.The erosion wear of the GN-3 laminated ceramic nozzlewas assessed in comparison with the CN-2 stress-free cera-mic nozzle by sand blasting. Fig. 9 shows the cumulativemass loss of the GN-3 and CN-2 nozzles in sand blastingprocesses. It can be seen that the cumulative mass loss con-tinuously increased with the operation time. Comparedwith GN-3 laminated nozzle, the CN-2 stress-free nozzleFig. 10. Photos of the worn inner bore profile of (a) the GN-3 laminatedFig. 11. Nozzle entry bore diameter variation with the erosion time for theGN-3 laminated nozzle and the CN-2 stress-free nozzle in sand blastingprocesses.nozzle, (b) the CN-2 stress-free nozzle after 540 min operation.Fig. 13 shows the SEM micrographs of the entry boresurface of the worn CN-2 stress-free nozzle. From theseSEM micrographs, dierent morphologies and fracturemodes of the nozzles can be seen clearly. The CN-2stress-free nozzle at the entry area failed in a highly brittlemanner, and exhibited a brittle fracture induced removalprocess. There are a lot of obvious pits located on the noz-zle bore surface indicating that brittle fracture took place.Characteristic SEM pictures taken on the eroded entrybore surface of the GN-3 laminated ceramic nozzle areshown in Fig. 14. It is shown that the appearance of theeroded areas of the laminated nozzle showed a relativesmooth surface by contrast with that of the stress-freenozzle.Ceramic nozzle failure by erosion wear is generallycaused by fracture owing large the tensile stress at the noz-zle entry zone 1115. Because the nozzle entrance regionsuers form severe abrasive impact, and generates largetensile stress, which may cause the subsurface lateral cracksand facilitates removal of the material chips. Thus, the ero-sion wear of the nozzle depends on the stress distribution inthe entry region. Once the maximum tensile stress exceedsthe ultimate strength of the nozzle material, fracture willoccur.The higher erosion wear resistance of the GN-3 lami-nated nozzle compared with that of the CN-2 stress-freenozzle can be analysed in terms of the formation of com-pressive residual stresses both on the entry area and onthe exit region. As calculated above, compressive residualFig. 12. Comparison of the erosion rate of the GN-3 laminated nozzle andthe CN-2 stress-free nozzle in sand blasting processes.D. Jianxin et al. / International Journal of Refractory Metals & Hard Materials 25 (2007) 263270 269Fig. 13. SEM micrographs of the entry bore surfaceFig. 14. SEM micrographs of the entry bore surfaceof the worn CN-2 stress-free ceramic nozzle.of the worn GN-3 laminated ceramic nozzle.stresses were formed at the entry and exit region of theGN-3 laminated nozzle in fabricating process from sinter-ing temperature to room temperature, which may partially8 Srinivasan S, Scatterrgood RO. Eect of erodent hardness on erosionof brittle materials. Wear 1988;128:13952.9 Shipway PH, Hutchings IM. The influence of particle properties on270 D. Jianxin et al. / International Journal of Refractory Metals & Hard Materials 25 (2007) 263270counteract the tensile stresses in the nozzle entry and exitsection resulting from external loadings. This eect maylead to the increase in resistance to fracture, and thusincrease the erosion wear resistance of the laminatednozzle.4. ConclusionsSiC/(W,Ti)C laminated ceramic nozzles were producedby hot pressing. The purpose is to reduce the tensile stressat the entry and exit area of the nozzle during sand blastingprocesses. Particular attention was paid to the erosion wearof this kind laminated ceramic nozzle. Results showed thatthe laminated ceramic nozzles have superior erosion wearresistance to that of homologous stress-free ceramic nozzle.The mechanism responsible was explained as the formationof compressive residual stresses both at the entry area andat the exit region of the laminated ceramic nozzle in fabri-cating process, which may partially counteract the tensilestresses resulting from external loadings. Laminated struc-ture in ceramic nozzles is an eective way to improve theerosion wear resistance of the stress-free ceramic nozzles.AcknowledgementsThis work