核动力工程

Experimental and Predictive Study of Pressure Drop in Low-flow Sub-cooled Boiling

SUN Qi, ZHAO Hua, XI Zhao, WANG Xiaojun, JIANG Xulun, YANG Ruichang

2005, 26(4): 305-311.

Abstract(9)

Abstract:
This paper presents the experimental study of the pressure drop for low-flow forced circula- tion in medium pressure sub-cooled boiling. The average void fraction is also measured in this experiment. Based on the experimental results, predictive investigation on pressure drop in low-flow sub-cooled boiling is carried out in this paper. The investigation shows that the pressure drops in low-flow sub-cooled boiling are dominated by pressure drop due to static head. Since the pressure drop due to static head are strongly affected by void fraction, it is very important to select the calculation model for void fraction. The Saha model and Levy model cannot be used to determine the void fraction for the calculation of pressure drop reliably. The NVG model and the true mass quality model proposed by the authors can be used to calculate the void frac- tion for the calculation of pressure drop in low-flow sub-cooled boiling correctly. Through the investigation, the proper method for the calculation of pressure drop in steam-water low-flow sub-cooled boiling with forced circulation is suggested in this paper.

Predictive and Experimental Study of Cross-Section Average Void Fraction in Sub-cooled Boiling with Natural Circulation

XI Zhao, SUN Qi, CHEN Jun, WU Xiaohang, JIANG Xulun, ZHAO Hua

2005, 26(4): 312-316,322.

Abstract(9)

Abstract:
Sub-cooled average void fraction in natural circulation is investigated using high-temperature high-pressure RBI optical probe in this paper. The experimental data are compared with the existing Saha model, Levy model and Sun mass true quality model. The result shows that these models based on forced circulation do not fit in the natural circulation. The analyses of the experimental data in this paper indicate that the void fraction in natural circulation is higher than that in forced circulation. In addition, the Sun mass true quality model is improved in this paper, and the improved model agrees quit well with the experimental data in natural circulation .

Experimental Study of Flow Instability in a Natural Circulation System with Sub-cooled Boiling

YANG Ruichang, WANG Yanwu, WANG Fei, TANG Hong, SHI Deqiang, LU Zhongqi

2005, 26(4): 317-322.

Abstract(11)

Abstract:
Experimental study has been performed to investigate the flow instability in a natural circula- tion system with sub-cooled boiling by using Freon-12 as the working medium. In the experiments, two kinds of flow instability, flow instability with high frequency and flow instability with low frequency, were found for most conditions. It is shown that the flow instability with high frequency belongs to acoustic oscillation and the flow instability with low frequency is density wave instability. In the experiments the effect of the parameters of the working medium on the onset of the flow instabilities in the system were investigated. The stability boundaries were determined through the experiments. By means of dimensional analysis of integral equations, the common correlations describing the threshold condition of onset of the flow instabilities were obtained.

Propagation of Pressure Wave for Bubbly Flow in Vertical Upward Tube

BAI Bofeng, HUANG Fei, GUO Liejin, WANG Xianyuan

2005, 26(4): 323-326.

Abstract(9) PDF(0)

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Experimental investigation was carried out to study the pressure wave speed and its attenua- tion for gas-liquid bubbly flow in vertical upward tube. In order to improve the measurement accuracy of the pressure wave, a setup was designed to adjust the frequency of the pressure force acting on the piping flow without changing the two-phase flow regime. The propagation of the two-phase flow pressure wave was measured with several pressure transmitters mounted flush to the pipe wall along the flow direction. The re- sults showed that the wave speed in bubbly flow decreased fleetly with the void fraction and decreased slowly when void fraction was more than 0.05. The attenuation had increased continuously with the void fraction. The flow velocity of the fluid mixture had not any effect on the propagation of pressure wave. Both the wave speed and attenuation coefficient had close relationship with the perturbation frequency, which increased with the disturbed frequency under low value range. A new phenomenon about critical disturbed frequency of the pressure wave dispersion in bubbly flow was validated in the present experimental investigation, which the dispersion of pressure wave would disappear under the perturbation frequency greater than a critical value. The critical frequency was about 300 Hz in the experimental test.

Qualification and Improvement of CATHARE 2V2.5 Flashing Model with Critical Flow Rate Experiments Data

CAO Nian, Isabelle DOR

2005, 26(4): 327-331.

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In the paper, the qualification of flashing models of CATHARE 2 V2.5 revision 5 （Rev.5） and revision 6.1（Rev.6.1） is carried out. The concerned critical flow rate experiments include BETHSY nozzle and Super-Moby-Dick （SMD） nozzle tests. The calculated results with Rev.6.1 and with Rev.5 are compared in the paper. On the whole, a good agreement can be shown using two revisions. The prediction of critical flow rate using Rev.6.1 is better than that using Rev.5. For SMD nozzle tests, the Rev. 6 results indicate a better agreement with the experimental data. But for BETHSY nozzle tests, the prediction of Rev.6.1 is over-estimated. The sensitivity study for improving the flashing model is also introduced in the paper.

3-D Numerical Simulation of Stripping and Stratification in Mixing T-Junction

LU Donghua, CUN Songshouqing

2005, 26(4): 332-334,389.

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3-D numerical simulation on flow regime has been performed for the equal diameter T-junction with different inlet temperatures for primary and branch pipes by AQUA code to study the stripping and stratification phenomenon. The results show that the inlet branch flow vertically sticks into the primary pipe and only a very narrow channel at the downside of primary pipe is left for the primary flow to pass through. A vortex existing just after this vertical branch flow at the upper side of the primary pipe greatly shrinks the flow area both for the primary flow and the branch flow, thus they are accelerated in this narrow channel. Temperature distribution has been investigated too. The temperature gradient indicates that the mix- ing at the upwind of the branch jet is fierce, but the mixing mainly happens at the downstream of the primary pipe.

Comparative Research on Steam-Water Two-Phase Flow Instabilities between Internally Ribbed Tubes and Smooth Tubes

GAO Feng, LUO Yushan, CHEN Tingkuan, LU Donghua, LI Huixiong

2005, 26(4): 335-339.

Abstract(9) PDF(0)

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This paper compared the effects of two types of tubes, the internally ribbed tubes and the smooth tubes, on the two-phase flow instabilities in parallel inclined tubes based on the experimental investi- gation in high pressure test loops. Experimental results showed that the system parameters had important ef- fects on the two-phase flow instabilities both in the two types of tubes. The thresholds of heat flux of pressure drop oscillation in smooth tubes are smaller than that in the internally ribbed tubes; otherwise, the thresholds of density wave oscillation in internally ribbed tubes are smaller than that in the smooth tubes. Non-dimensional correlations of thresholds of heat flux both in the internally ribbed and the smooth tubes had been provided through the regression calculation of test data.

Theoretical Investigation of Flow Regime for Boiling Water Two-Phase Flow in Horizontal Rectangular Narrow Channels

ZHANG Chunwei, QIU Suizheng, YAN Mingyu, WANG Bulei, NIE Changhua

2005, 26(4): 340-343,371.

Abstract(7) PDF(0)

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The flow regime transition criteria for the boiling water two-phase flow in horizontal rectan- gular narrow channels（1×20mm,2×20mm） were theoretically explored. The discernible flow patterns were bubbly, intermittent slug, churn, annular and steam-water separation flow. By using two-fluid model, equa- tions of conservation of momentum were established for the two-phase flow.New flow-regime criteria were obtained and agreed well with the experiment data.

Heat Transfer Enhancement in Rectangular Narrow Channel with Periodically Mounted Longitudinal Vortex Generators on One Sidewall

WANG Ling, CHEN Qiuyang, ZHOU Yangeng, WANG Qiuwang, HUANG Yanping, XIAO Zejun

2005, 26(4): 344-347,359.

Abstract(11) PDF(0)

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Repeated ribs mounted on sidewall in channels are often used to enhance convective heat transfer. In this paper, the heat transfer and fluid flow in a rectangular narrow channel with periodicallymounted Longitudinal Vortex Generators （LVGs） on one sidewall was investigated experimentally in the range of Re=3×10³ and Re=2×10⁴. The effect of flow direction on the heat performance was also con-ducted. It was found that the LVGs are able to greatly improve the comprehensive heat transfer performance. And under three kinds of comparison criterion （Identical Mass Flow-IMF, Identical Pressure Drop-IPD, Iden- tical Pumping Power-IPP）, the heat transfer performance of parallel-flow was a little better than that of counter-flow.

Numerical Simulation of Water Film Flowing on Corrugated Separator Plate

TIAN Ruifeng, ZHUANG Yaping, WANG Xianyuan, CHEN Junliang

2005, 26(4): 348-351,363.

Abstract(9) PDF(0)

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The effect of separator corrugated-plate water-film flow on the forming of secondary droplets was studied by numerical method. By analyzing the flow character of water film on separator corrugated plate, and using reasonable simplifying and hypothesis, water film physical model and mathematical model were developed. Using finite volume method, convection term was discretized with two-order upwind dif- ference algorithm, and diffusion term was discretized with central difference algorithm. ADI （Alternat- ing-Direction Implicit） solution was used. By numerical simulating movement of water film on separa- tor-corrugated plate, under main steam transverse sweep situation, the relations between the water film pa- rameters and wet steam velocity, humidity had been obtained.

Follow-up Analysis of HFETR Burn-up By CELL/CPL493 Code

YAO Dong, YU Yingrui, SHEN Xirong, LI Datu

2005, 26(4): 352-355.

Abstract(9) PDF(0)

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This paper briefly introduced the methodology of the CELL/CPL493 code system, and follow-up analysis of the multi-cycles burn-up for High Flux Engineering Test Reactor （HFETR） had been perform by using of the CELL/CPL493 code system. At the same time, the comparisons of the critical control rod positions at cold case and operation condition between the calculation values and measured ones had been presented. The numerical results showed that the maximum deviation in keff was less than 1%, which was very satisfactory.

Research on Vibration and Noise Issues of Nuclear Pipesdue to Orifice Cavitation

MAO Qing, XIANG Wenyuan, ZHANG Yixiong, WANG Wei

2005, 26(4): 356-359.

Abstract(9) PDF(0)

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Violent vibration and noise symptoms have been found in a nuclear piping system, which is caused by the cavitation after a throttle orifice. The research and engineering modification of this issue are presented in this paper. Intensive investigation with numerical and experimental methodologies has been made to find the root cause of the malfunction, and then the modification ways are proposed based on the conclusions of root cause analysis. Field investigation and evaluation after system modification have shown great suppression of the vibration and noise symptoms, while the system function and structure integrity have been validated to meet the requirement of original design code, which demonstrates that the system modifi- cation issuccessful. Moreover, a “numerical simulation priority” approach is introduced in the research work and the application of this approach has significantly reduced the time and cost of the whole project.

Flow Induced Vibration Analysis of Thermo-well at Main Pipe of Reactor Coolant Loop

ZANG Fenggang, LIU Wenjin

2005, 26(4): 360-363.

Abstract(10) PDF(0)

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There are mainly two excitation mechanisms in the vibration of the thermo-well at the main pipe of reactor coolant loop under cross flow: turbulence and vortex shedding. The natural frequencies of the G1″and G1″ 1/4 thermo-well and the vortex shedding frequencies are calculated, respectively, in this paper. The vortex shedding lock-in is analyzed for two different thermo-wells, and then the flow induced vibration fatigue of the thermo-well is studied using a simplified engineering approach.

Microstructure Evolution of Oxide Films Formed on Zircaloy-4 during Autoclave Tests

ZHOU Bangxin, LI Qiang, YAO Meiyi, LIU Wenqing, CHU Yuliang

2005, 26(4): 364-371.

Abstract(9) PDF(0)

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The microstructure and crystal structure of oxide films in different depth of oxide thickness, and the morphology of fracture surface of oxide films, which are formed on Zircaloy-4 specimens during the autoulave tests in deionized water at 360 ℃/ 18.6MPa, have been investigated by transmission electron mi- croscopy, scanning electron microscopy and scanning probe microscopy. The results show that except the stable monoclinic crystal structure, the meta-stable phases including cubic, tetragonal and amorphous phases can be observed in the bottom layer of oxide films due to the presence of defects induced by the compressive stress in oxide crystals during the formation of zirconium oxide. Under the action of temperature, stress and time, the diffusion, annihilation and condensation of defects as vacancies and interstitials will be taken place in the middle and surface layer of oxide films. The inner stress of oxide crystals will be relaxed and the meta-stable phases will transform to the stable phase. Vacancies absorbed by grain boundaries form the clus- ters of pores in nanoscale, which will weaken the bonding force between grains. In this case, the grains will become gradually spherical due to the action of surface tension. Based on the formation of the clusters of pores and the development of cracks in oxide films,the phenomenon of corrosion transition will be induced due to the loss of protective characteristic of oxide films. This is an inevitable result caused by the micro- structure evolution of oxide films during the autoulave tests.

Effect of Hydrogen and Hydride on Fatigue Cracking Rate of Zirconium-Based Alloys and Its Estimation

GOU Yuan, LI Yanrong, YING Shihao

2005, 26(4): 372-376.

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In this paper, compact toughness samples are used to study the fatigue cracking prolongation behaviors of Zr-4 and Zr-Sn-Nb alloys with different hydrogen contents. Test results indicate that the hydro- gen contents have little effect on the fatigue cracking rate, and fracture behavior is controlled by the nature fatigue cracking mechanism, which include crack budding, stable prolonging and rapid ultimate fracture. According to the mechanism of fatigue cracking, the relationship of fatigue cracking rate （da/dN） and general properties of materials has been induced. In term of this relationship, calculating values of fatigue crack rate of zirconium-based alloys are consonant with the experimental values.

Structure Analysis of Film Formed by Reaction of CO₂ and Zirconium Hydride

ZHAO Ping, PENG Qian, KONG Xianggong, ZOU Congpei

2005, 26(4): 377-379,405.

Abstract(8) PDF(0)

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A film with a thickness of 3～5μm was formed by the reaction of CO₂ and zirconium hydride. Observation of the crosssection of the film by SEM found that the surface was combined tightly with the zirconium hydride. The film could be a hydrogen permeation barrier. XPS analysis showed that there were Zr, C and O in the film. Besides the ZrO₂ baddeleyite, some O-H and C-H chemical bonding also existed in the film.

Investigation on High Temperature Fretting Wear Behaviour of Ni-Cr Coatings on TiAlZr Alloy

LIU Hanwei, HUANG Kunpeng, ZHU Minhao, QIU Shaoyu, ZHOU Zhongrong

2005, 26(4): 380-383.

Abstract(8) PDF(0)

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TiAlZr alloy and its thermal spraying Ni-Cr coatings are tested on the fretting wear machine and investigated comparatively at different temperatures. It is showed that when the fretting is in the gross-slip regime, temperature has great effect on the fretting wear. With temperature increasing, in the gross-slip regime, wear-resistant capability of TiAlZr titanium alloy decreases; however, that of thermal spraying Ni-Cr coatings, which is excellent particularly at 400℃ because of oxide films formation, increases. Frictional properties are improved with thermal spraying Ni-Cr coatings on TiAlZr alloy substrate.

Stress Corrosion Cracking of Solution-Annealed Nitrogen- Containing Austenitic Stainless Steels in High Temperature Water Environments

LI Guangfu, HUANG Chunbo, LI Jingmin, YANG Wu, WEN Yan

2005, 26(4): 384-389.

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Effects of electrode potential and Cl^- content in water on stress corrosion cracking （SCC） of solution-annealed nitrogen-containing stainless steels 304NG and 316LN in high temperature water environ- ments at 250℃ were studied by using slow strain rate test and high temperature electrode potential control technology. Results showed that, for steel in each water environment, the susceptibility to SCC increased with the increasing of potential and there was a minimum potential for SCC （E_C） below which no SCC oc-curred. The E_C decreased with the rise of Cl^- content in water, that is, the environmental range suitable for SCC increased. In the solution containing 5mg/L Cl^-, the E_C of 304NG was in the range of 0 ～ +200mV（SHE） above which transgranular SCC occurred, which means that this steel may exhibit SCC at such Cl^- content when the water contained high content of oxygen. When Cl^- content was increased to 50 mg/L, E_C decreased to less than -700 mV（SHE）, which means that this steel may exhibit SCC at such Cl^- content even when the oxygen in water has been well eliminated. 316LN exhibited higher resistance to SCC than 304NG, as its E_C was in the range of +300 ～ +400mV（SHE）. The main cracking of 316LN was transgranular.

Research on General Corrosion Property of 304NG Stainless Steel

JIANG E, WEN Yan, LIU Ranchao, HE Yanchun

2005, 26(4): 390-392.

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The circulating water corrosion test of 304NG stainless steel has been performed in the MARS loop for 1500 h.The quantitative estimation for general corrosion rate of the 304NG stainless steel is given. The test result showed that the general corrosion rate of 304NG stainless steel is 1.40mg（dm²ˇ30d）（for plate） and 1.91 mg/（dm²ˇ30d）（for forging） under the simulation primary circulating water environment of nuclear reactor. For 0Cr18Ni10Ti, it is 4.44mg/（dm²ˇ30d） and 4.65mg/（dm²ˇ30d）, respectively. The general corrosion rate of 304NG is lower than that of 0Cr18Ni10Ti under the simulation primary circulating water environment of nuclear reactor.

Fretting Behaviour of 1Cr13 Stainless Steel from Room Temperature to 400℃ in Gross Slip Regime and Slip

LIU Hanwei, QIU Shaoyu, ZHU Minhao, HUANG Kunpeng, ZHOU Zhongrong

2005, 26(4): 393-396.

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Fretting wear behaviour of the 1Cr13 stainless steel from room temperature to 400℃ were investigated on a Deltalab-Nene7 fretting wear test rig. Dynamic analysis and microscopic examinations have shown that the fretting behavior depended strongly on the fretting regime. Coefficient of friction and wear volume reduced as the increasing of temperature in slip regime, and little difference was observed in partial slip regime. The fretting wear mechanism is analyzed: As the temperature increases, an oxide film forming on the surface of 1Cr13 stainless steel for the high temperature oxidizing. The crack on oxide film generates and fractures under the effect of fretting, and the crack propagates parallel to the surface. The wear debris is de- tached from the substrate by the repeated stress action.

Study on Microstructure Transformation of 17-4PH Stainless Steel after Long-Term Aging at 350℃

ZOU Hong, WANG Jun, LI Cong, ZUO Rulin, QIU Shaoyu, SHEN Baoluo

2005, 26(4): 397-401,409.

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The transformation of microstructure with the extension of aging time on the type of 17-4PHstainless steel at 350℃ was studied in this paper by X-ray diffraction and transmission electron microscope. The results showed that there was the matrix of lath martensite and the nano-metric precipitates of ε-Cu and secondary carbide, M₂₃C₆, after the type alloy subjected to solution treatment and temper treatment. When the alloy aged at 350℃ for about 4200 h, the α-α’ spinodal decomposition occurred along the grain boundary and some reversed austenite was transformed. With the age time extended to 11000 h, the spinodal decomposition and G-phase, which consisted of complex nickel silicide, precipitation occurred in matrix at this intermediate temperature. Some sigma phase was also observed.

Microstructural Characterization of Brazed Joints between Titanium and Stainless Steel

YANG Jing, ZHU Changgui, WANG Fei, ZHU Jinxia, LIU Xiaorong

2005, 26(4): 402-405.

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Optical microscopy, scanning electron microscopy, EDXA, micro-hardness and mechanical properties tests were adopted to investigate the microstructural characterization of brazed joints between tita- nium alloy, Ag95CuNiLi and stainless steel. The results showed that three layers of inter-metallic compounds had formed at the side of stainless steel/filler metal, and two zones with different microstructures had been produced at the side of titanium alloy/filler metal. At the same time, Ag diffused along the grain boundary of titanium alloy. In brazed joints, Ti and Cu enriched at the side of stainless steel, and Cu enriched near the ti- tanium alloy. The center area of the fillet is basically pure silver. Except that at the diffusion layer of the stainless steel/filler metal, the micro-hardness of other areas did not increase compared with the hardness before brazing. Joint failure analysis showed that the weakest occurred at the place near the stainless steel.

Corrosion Behavior of Ti-5%Ta Alloy in Simulated Solution for Dissolving Spent Fuel

XU Xiaoxiao, CUI Lan, QIU Shaoyu, LI Sifan, SHENG Zhongqi, TAI Jiang

2005, 26(4): 406-409.

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As the construction material of the reprocessing equipment for nuclear spent fuel, 000Cr25- Ni2 austenitic stainless steel is corroded seriously by the solution for dissolving spent fuel of power reactors. The tests show that the corrosion resistance of Ti-5%Ta alloy is by far superior to that of the 000Cr25Ni20 austenitic stainless steel. The reason is that a compact oxide film forms on the sample surface of Ti-5%Ta alloy, which plays a role in hindering corrosion development, and no oxide film is found on the sample sur- face of 000Cr25Ni2 austenitic stainless steel.

Effect of Pre-strain on Two-way Shape Strain in TiNi and TiNiCu Alloy

JIN Wei, WANG Jian, YAN Ying

2005, 26(4): 410-413,418.

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Effect of pre-strain on two-way shape memory strain of Ti49.2Ni50.8 and Ti50Ni43Cu7 alloy were investigated by tensile test and electrical resistance measurement. The results indicated that there ex- isted optimal pre-strain temperature and pre-strain value, at which the specimen exhibited maximum two-way shape memory strain. For Ti49.2Ni50.8 tensile specimens, the maximum two-way shape memory strain was 3.6% （pre-strain 14% at -60℃）, for Ti50Ni43Cu7 tensile specimens the maximum two-way shape memory strainwas 3.0% （pre-strain 12% at 20℃）。For Ti49.2Ni50.8 ring shape specimens, the maximum two-way shape memory strain was 4.1% （pre-strain 13.7% at -60℃）.

Fretting Wear Behaviour of TiC/Ti（C, N）/TiN Multi-Layer Coatings at Elevated Temperature in Gross Slip Regime

LIU Hanwei, QIU Shaoyu, ZHOU Tong, HUANG Kunpeng, ZHU Minhao, ZHOU Zhongrong

2005, 26(4): 414-418.

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TiC/Ti（C, N）/TiN multi-layer coatings are prepared on the 1Cr13 stainless steel substrate by the technique of Chemical Vapour Deposition, and the fretting wear behaviour of 1Cr13 stainless steel and TiC/Ti（C, N）/TiN coatings are investigated and studied contrastively from 25℃ to 400℃ in the gross slip regime. It showes that the temperature has great influence on the fretting wear in the gross slip regime for the 1Cr13 stainless steel but little for TiC/Ti（C, N）/ TiN multi-layer coatings. With the temperature increasing, the friction coefficient and the wear volume of the 1Cr13 alloy decreases and the wear volume of TiC/Ti（C, N）/TiN multi-layer coatings is invariant. TiC/Ti（C, N）/TiN multi-layer coatings have better wear-resistant capability than the 1Cr13 stainless steel, but the wear volume of the substrate increases greatly because of the grain-abrasion resulted from hard debris when TiC/Ti（C, N）/TiN multi-layer coatings are ground off.

2005 Vol. 26, No. 4