• Title/Summary/Keyword: surface microhardness

Search Result 320, Processing Time 0.021 seconds

Electrolytic Boronizing on Carbon Steels in Fused Slat of Borax and Sodium Chloride Mixture (붕사와 염화나트륨 혼합용융욕에서 탄현강의 전해붕화처리)

  • 이두환;김정기;김한삼;김수식
    • Journal of the Korean institute of surface engineering
    • /
    • v.30 no.1
    • /
    • pp.23-32
    • /
    • 1997
  • The electrolytic boronizing on carbon steels in the mixture of $Na_2B_4O_7$ and NaCl was conducted at 750~$950^{\circ}C$ for 1~6 hours under 0.5A/$\textrm{cm}^2$ current density. The micorostructrure and microheredness of boronized layer was also studien. The effect of the additive such as $CaCl_2$ or NaOH on the formation of boronized layer was also investigated. The boronized layer were composed of two sublayers, i.e., FeB and $Fe_2B$ , which have tooth structure. the average layer thinknesses of the low carbon steel and SM45C boronized at $900^{\circ}C$ for 4hours were 153 and 138 $\mu\textrm{m}$, respectively. The thickness of the twosublayers was significantly increased with increasing boronizing temperature. To obtain a single $Fe_2B$ layer without FeB sublayer, the boronized materials ware homegenized at $950^{\circ}C$ for 4 hours. It was fount that the single layer with a microhardness Hv$\thickapprox$ 1120 -1250 was formed. The calculated activation energies for formation of boronized layer on the low carbon steel and SM45C were 18.7 and 12.6 Kcal/mol, respectively.

  • PDF

Nanoindenter Test of 680MPa Dual Phase Steel Charged with Hydrogen (수소주입시킨 680MPa DP강의 나노인덴터 시험)

  • Choi, Jong-Woon;Park, Jae-Woo;Kang, Kae-Myung
    • Journal of the Korean institute of surface engineering
    • /
    • v.47 no.1
    • /
    • pp.33-38
    • /
    • 2014
  • Nanoindentater tests were conducted to conducted nanoindentation microhardness of the individual phase of ferrite and martensite of 680MPa dual-phase (DP) steel charged with hydrogen. Hydrogen was charged by electrochemical method with current densities of 150, $200mA/cm^2$ for charging times of 5, 10, 25, 50 hours, respectively. Nanoindenter test results showed that the nanoindentation microhardnesses of ferrite phase of DP steel were varied from min. 1.58 GPa to max. 2.82 GPa, and the nanoindentation microhardnesses of martensite phase varied from min. 3.19 GPa to max. 5.16 GPa with the variation of hydrogen charging conditions. It was observed that the variations of the nanoindention microhardnesses of martenstie phase were higher than those of ferrite phases. It was thought that martensite phase in the 680MPa DP steel was more sensitive than ferrite phase to hydrogen embrittlement.

Cr - Mo鋼 熔接 後熱處理材 의 勞破壞 에 關한 硏究

  • 박재규;김석원;김연식
    • Journal of Welding and Joining
    • /
    • v.3 no.2
    • /
    • pp.16-26
    • /
    • 1985
  • Post weld heat treatment(PWHT), at more than 600.deg. C, is essential to remove residual stress and hydrogen in weld HAZ and improve fatigue characteristics. However, residual stress during PWHT is responsible for PWHT embitterment and it promotes precipitation of impurities to grain boundary. In this paper, the effect of stress simulated residual stress on fatigue failure was evaluated by fatigue test, microhardness test and fractograph. The obtained results are summarized as follows; (1) The fatigue crack growth rate(da/dN) of parent and heat treated parent was affected by microstructure due to heat treatment and it depended on stress intensity factor (.DELTA.k). (2) The fatigue strength of weld HAZ was dependent on applied stress during PWHT and da/dN after PWHT was slower than as-weld. (3) Softening amount of weld HAZ was bigger than any other due to PWHT. Hardness value of weld HAZ was affected by heat treatment under the applied stress of 10 $kgf/mm^2$, but beyond 20 $kgf/mm^2$ it was increased by the applied stress rather than heat treatment. (4) Beyond the applied stress of 20 $kgf/mm^2$ during PWHT, intergranular fracture surface was observed and its amount was increased with applied stress during PWHT. (5) Effect of applied stress during PWHT on aspect of fracture surface was larger rather than that on fatigue crack growth behavior.

  • PDF

Effect of Si on the Microstructure and Mechanical Properties of Ti-Al-Si-C-N Coatings (Si 함량에 따른 Ti-Al-Si-C-N 코팅막의 미세구조와 기계적 특성의 변화에 관한 연구)

  • Hong, Young-Su;Kwon, Se-Hun;Kim, Kwang-Ho
    • Journal of the Korean institute of surface engineering
    • /
    • v.42 no.2
    • /
    • pp.73-78
    • /
    • 2009
  • Quinary Ti-Al-Si-C-N films were successfully synthesized on SUS 304 substrates and Si wafers by a hybrid coating system combining an arc ion plating technique and a DC reactive magnetron sputtering technique. In this work, the effect of Si content on the microstructure and mechanical properties of Ti-Al-C-N films were systematically investigated. It was revealed that the microstructure of Ti-Al-Si-C-N coatings changed from a columnar to a nano-composite by the Si addition. Due to the nanocomposite microstructure of Ti-Al-Si-C-N coatings, the microhardness of The Ti-Al-Si-C-N coatings significantly increased up to 56 GPa. In addition the average friction coefficients of Ti-Al-Si-C-N coatings were remarkably decreased with Si addition. Therefore, Ti-Al-Si-C-N coatings can be applicable as next-generation hard-coating materials due to their improved hybrid mechanical properties.

Electrodeposited Ni-W-Si3N4 alloy composite coatings: Evaluation of Scratch test

  • Gyawali, Gobinda;Joshi, Bhupendra;Tripathi, Khagendra;Lee, Soo Wohn
    • Proceedings of the Korean Institute of Surface Engineering Conference
    • /
    • 2014.11a
    • /
    • pp.178-179
    • /
    • 2014
  • In this study, $Ni-W-Si_3N_4$ alloy composite coatings were prepared by pulse electrodeposition method using nickel sulfate bath with different contents of tungsten source, $Na_2WO_4.2H_2O$, and dispersed $Si_3N_4$ nano particles. The structure and microstructure ofcoatings was separately analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results indicated that nano $Si_3N_4$ and W content in alloy had remarkable effect on microstructure, microhardness and scratch resistant properties. Tungsten content in Ni-W and $Ni-W-Si_3N_4$ alloy ranged from 7 to 14 at.%. Scratch test results suggest that as compared to Ni-W only, $Ni-W-Si_3N_4$ prepared from Ni/W molar ratio of 1:1.5 dispersed with 20 g/L $Si_3N_4$ has shown the best result among different samples.

  • PDF

Effects of Amorphous Si3N4 Phase on the Mechanical Properties of Ti-Al-Si-N Nanocomposite Films Prepared by a Hybrid Deposition System (하이브리드 증착 시스템에 의해 합성된 나노복합체 Ti-Al-Si-N 박막 내 존재하는 Si3N4 비정질상이 기계적 특성에 미치는 영향)

  • An, Eun-Sol;Jang, Jae-Ho;Park, In-Uk;Jeong, U-Chang;Kim, Gwang-Ho;Park, Yong-Ho
    • Proceedings of the Korean Institute of Surface Engineering Conference
    • /
    • 2014.11a
    • /
    • pp.304-304
    • /
    • 2014
  • Quaternary Ti-Al-Si-N films were deposited on WC-Co substrates by a hybrid deposition system of arc ion plating (AIP) method for Ti-Al source and DC magnetron sputtering technique for Si incorporation. The synthesized Ti-Al-Si-N films were revealed to be composites of solid-solution (Ti,Al)N crystallites and amorphous $Si_3N_4$ by instrumental analyses. The Si addition in Ti-Al-N films affected the refinement and uniform distribution of crystallites by percolation phenomenon of amorphous silicon nitride, similarly to Si effect in TiN film. As the Si content increased up to about 9 at.%, the hardness of Ti-Al-N film steeply increased from 30 GPa to about 50 GPa. The highest microhardness value (~50 GPa) was obtained from the Ti-Al-Si-N film having the Si content of 9 at.%, the microstructure of which was characterized by a nanocomposite of $nc-(Ti,Al)N/a-Si_3N_4$.

  • PDF

A Behavior of Embrittlement at the Subsurface Zones of Multiphase Steels Charged with Hydrogen (수소주입시킨 다상조직강의 Subsurface Zone 내 취성화 거동)

  • Kang, Kae-Myung;Park, Jae-Woo;Choi, Jong-Un
    • Journal of the Korean institute of surface engineering
    • /
    • v.46 no.1
    • /
    • pp.48-53
    • /
    • 2013
  • In the present work, it was investigated a behavior of hydrogen embrittlement at the subsurface zones of 590 DP steels by using the micro-Vickers hardness test. The micro-Vickers hardnessess of DP steels were measured to evaluate the degree of embrittlement as the effective hardening depths of subsurface zones with hydrogen charging conditions. The results showed that the distributions of micro-Vickers hardness in width varied from maximum hardness 239.5 Hv to minimum hardness 174 Hv, while the depth of effective hardening layer at the subsurface zones of DP steels was from $320{\mu}m$ to $460{\mu}m$ with hydrogen charging conditions, respectively. It was proposed that the distribution of microhardness be used as the evaluation index of the degree of embrittlement. But the variations of martensite volume fractions were not affected along depth of hardening at the same changing time, hydrogen charging times were appeared as an effective factor of the degree of embrittlement. Therefore, the micro-Vickers hardness test is an attractive tool for evaluation of hydrogen embrittlement at the subsurface zones of these DP steels.

Characteristics of Friction Stir Welded AZ31 Mg Alloys with Shoulder Diameter and Rotating Speed (숄더 지름과 회전 속도에 따른 AZ31 마그네슘합금의 마찰교반접합 특성)

  • Jun, Sang-Hyuk;Ko, Young-Bong;Park, Kyeung-Chae
    • Journal of the Korean institute of surface engineering
    • /
    • v.46 no.1
    • /
    • pp.36-41
    • /
    • 2013
  • Friction stir welding (FSW) is a relatively new joining technique particularly for magnesium and aluminum alloys that are difficult to fusion weld. In this study, AZ31 Mg alloys were joined by FSW with shoulder diameter 11, 19 mm and rotating speed 900, 1200, 1500, 1800 rpm. The shoulder diameter and welding speed depended on the heat input during FSW process. As a result, the microstructures of stir zone were a fine grain by dynamic recrystallization. According to the larger shoulder diameter and the higher rotating speed, refined grain sizes of stir zone were grown by higher heat input, and the microhardness of stir zone was lower. The tensile strength at the shoulder diameter 19 mm, rotating speed 900 rpm was obtained maximum value. This value compared with the base metal was over 93%.

A STUDY ON THE REMINERALIZATION OF ARTIFICIAL CARIOUS LESION AFTER FLUORIDE-CONTAINING SEALANT APPLICATION ON BOVINE ENAMEL (불소함유 전색제 도포에 따른 인공 우식병소의 재석회화에 관한 연구)

  • Kim, Jae-Gon;Baik, Byeong-Ju
    • Journal of the korean academy of Pediatric Dentistry
    • /
    • v.25 no.3
    • /
    • pp.569-575
    • /
    • 1998
  • The purpose of this study was to evaluate the remineralization effects of fluoride-containing sealant on the artificially created enamel carious lesions. The fluoride release from the specimen of fluoride-containing sealants, the effect on enamel acid solubility and micro-hardness from the experimental sealants when applied to carious enamel surfaces were investigated. The obtained results were as follows; 1. Fluoride was a rapid rate of release during the first day, with the amount diminishing with time. The amount of fluoride released from Fuji Ionomer type III was higher than that from Teethmate-F and Helioseal-F during the 28 days of immersion(P<0.05). 2. The enamel solubility of carious enamel surface was higher than that in the Teethmate-F, Helioseal-F, and Fuji Ionomer type III (P<0.05), and there was no significant difference with Teethmate-A and Helioseal(P>0.05). 3. The microhardness value of carious enamel surface was lowest. However, there was no significant difference between the other sealants with respect to their effects on enamel hardness(P>0.05).

  • PDF

A STUDY ON WEAR AND CORROSION RESISTANCE OF CrN$_{x}$ FILMS BY CATHODIC ARC ION PLATING PROCESS

  • Han, Jeon-G.;Kim, Hyung-J.;Kim, Sang-S.
    • Journal of the Korean institute of surface engineering
    • /
    • v.29 no.5
    • /
    • pp.545-548
    • /
    • 1996
  • $CrN_x$ films were deposited on SKD61 and S45C by cathodic arc ion plating process. In this study, the microstructure, microhardness, a hesion, wear and corrosion properties of the CrNx films were studied for various nitrogen partial pressures and the results were compared with those from the electroplated hard Cr. The crystal structure of the films was characterized by X-ray diffraction. Wear tests were performed under no lubricant condition at atmosphere by ball-on-disc type tribotester. Corrosion resistance of the films were studied by electrochemical corrosion test, measuring current demsity-potential curves. The results indicated that the $CrN_x$ films formed using ion plation method showed higer hardness and lower current density, friction coefficient than electroplated hard Cr. Consequently, the application of the CrNx coationgs by ion plating which is free of environmental pollution, is expected to improve lifetime of components in industrial practice.

  • PDF