Авторизация
Логин:
Пароль:
Регистрация
Забыли свой пароль?

Особенности определения твердости и трещиностойкости твердых сплавов при разных нагрузках вдавливания пирамиды


М. И. Дворник, Т. Б. Ершова, Е. А. Михайленко, В. О. Крутикова; № 9 (83), 09.2017

Аннотация:

Рассмотрен размерный эффект, возникающий при уменьшении нагрузки с 50 до 0,05 кгс в процессе измерения твердости по Виккерсу среднезернистого (WC-8Co), субмикронного (WC-8Co-1Cr3C2) и ультрамелкозернистого (WC-8Co-0,4VC-0,4Cr3C2) твердых сплавов, а также стандартных твердых сплавов ВК6ОМ и Т15К6. Прирост твердости в результате размерного эффекта достигает 14 – 16 %. Показано, что возле отпечатков твердомера возникают возвышения, которые искажают результаты измерений. Установлено наличие обратной зависимости твердости от размера отпечатка индентора. Наибольший размерный эффект наблюдается у более твердого ультрамелкозернистого сплава. Проведено сравнение результатов измерения трещиностойкости методом Палмквиста с помощью оптического и растрового микроскопов. Отмечено, что формирование трещин по схеме Палмквиста происходит под воздействием нагрузок, превышающих определенную величину, которая зависит от трещиностойкости сплава. Отжиг не оказывает значительного влияния на результаты измерения твердости и трещиностойкости. Полученные результаты подтверждают снижение трещиностойкости при повышении твердости за счет уменьшения среднего размера зерна WC при переходе от среднезернистых твердых сплавов к субмикронным и ультрамелкозернистым сплавам.

Ключевые слова: твердость Виккерса; трещиностойкость Палмквиста; индентирование; размерный эффект; ультрамелкозернистый твердый сплав.

Features of Hardness and Crack Resistance Determination in Hard Alloys under Different Loading of Indenting Pyramid

M. I. Dvornik, T. B. Ershova, E. A. Mikhailenko, and V. O. Krutikova

The size effect arising upon the load decrease from 50 kgf up to 0.05 kgf in measurements of the Vickers hardness for medium-grained (WC-8Co), submicron (WC-8Co-1Cr3C2) and ultrafine-grained (WC-8Co-0.4VC-0.4Cr3C2) hard alloys, as well as standard hard alloys T15K6 and VK6OM is considered. An increase in hardness resulting from the size effect attains 14 – 16%. Presence of the elevations near the penetrator indentation distorts the measurement results. The inverse dependence of hardness on the size of indentation is demonstrated. The largest dimensional effect is observed for the hardest ultrafine-grained alloy. The results of the fracture resistance measurements using Palmquist method for optical and raster microscopes are compared. It is shown that crack formation in the Palmquist scheme occurs under the impact of loads exceeding a critical value, which depends on the fracture toughness of the alloy. Annealing does not have a significant effect on the results of hardness and fracture toughness measurements. The results confirm a decrease in the crack resistance with increasing hardness due to reduction in the average grain size of WC sample when going from medium-grained hard alloys to submicron and ultrafine-grained alloys.

Keywords: Vickers hardness; Palmquist crack toughness; indentation; size effect; ultrafine hard alloy.

1. Liu Xuemei, Song Xiaoyan, Zhang Jiuxing, Zhao Shixian. Temperature distribution and neck formation of WC-Co combined particles during spark plasma sintering / Mater. Sci. Engin. A. 2008. Vol. 488. P. 1 – 7.

2. Fukatsu Tamotsu, Kobori Keiichi, Ueki Mitsuo. Micro-grained cemented carbide with high strength / Int. J. Refract. Met. Hard Mater. 1991. Vol. 10. Issue 2. P. 57 – 60.

3. Spriggs G. E. A History of Fine Grained Hardmetal / Int. J. Refract. Met. Hard Mater. 1995. Vol. 13. P. 241 – 255.

4. Gille G., Szesny B., Dreyer K., Van den Berg H., Schmidt J., Gestrich T., Leitner G. Submicron and ultrafine grained hardmetals for microdrills and metal cutting inserts / Int. J. Refract. Met. Hard Mater. 2002. Vol. 20. P. 3 – 22.

5. Dvornik M. I., Zaytsev A. V., Ershova T. B. Improvement of strength and hardness of submicron cemented carbide WC-8%Co-1%Cr3C2 due to the carbonization during sintering process / Vopr. Materialoved. 2011. Vol. 68. N 4. P. 81 – 88 [in Russian].

6. Suna H. Q., Irwana R., Huanga H., Stachowiak G. W. Surface characteristics and removal mechanism of cemented tungsten carbides in nanoscratching / Wear. 2010. Vol. 268. P. 1400 – 1408.

7. Saito Hiroyuki, Iwabuchi Akira, Shimizu Tomoharu. Effects of Co content and WC grain size on wear of WC cemented carbide / Wear. 2006. Vol. 261. P. 126 – 132.

8. Jia K., Fischer T. E. Sliding wear of conventional and nanostructured cemented carbides / Wear. 1997. Vol. 203 – 204. P. 310 – 318.

9. Bonny K., Baets P. D., Vleugels J., Huang S., Wan der Biest O., Lauwers B. Impact of Cr3C2 VC additions on dry sliding friction and wear response of WC-Co cemented carbides / Wear. 2009. Vol. 267. Issue 9 – 10. P. 1642 – 1652.

10. Krakhmalev P. V., Adeva Rodil T., Bergstrom J. Influence of microstructure on the abrasive edge wear of WC-Co hardmetals / Wear. 2007. Vol. 263. P. 240 – 245.

11. Allen C., Sheen M., Williams J., Pugsley V. A. The wear of ultrafine WC-Co hard metals / Wear. 2001. Vol. 250. P. 604 – 610.

12. Abele E., Frohlich B. High speed milling of titanium alloys / Adv. Prod. Engin. Management. 2008. N 3. P. 131 – 140.

13. Engqvist H., Jacobson S., Axen N. A model for the hardness of cemented carbides / Wear. 2002. Vol. 252. P. 384 – 393.

14. Xu Zhi-Hui, Agren John. A modified hardness model for WC-Co cemented carbides / Mater. Sci. Engin. A. 2004. Vol. 386. P. 262 – 268.

15. Cha Seung I., Lee Kyong H., J. Ryu Ho, Hong Soon H. Analytical modeling to calculate the hardness of ultra-fine WC-Co cemented carbides / Mater. Sci. Engin. A. 2008. Vol. 489. P. 234 – 244.

16. Makhele-Lecala L., Luiyckx S., Nabarro F. R. N. Semi-empirical relationship between hardness, grain size and mean free path of WC-Co / Int. J. Refract. Met. Hard Mater. 2001. Vol. 19. P. 245 – 249.

17. Jia K., Fischer T. E., Gallois B. Microstructure, hardness and toughness of nanostructured and conventional WC-Co composites / Nanostruct. Mater. 1998. Vol. 10. Issue 5. P. 875 – 891.

18. Liu Binghai, Zhang Yue, Ouyang Shixi. Study on the relation between structural parameters and fracture strength of WC-Co cemented carbides / Mater. Chem. Phys. 2000. Vol. 62. Issue 1. P. 35 – 43.

19. Wei Chongbin, Song Xiaoyan, Fu Jun, Liu Xuemei, Wang Haibin, Gao Yang, Wang Yao. Simultaneously high fracture toughness and transverse rupture strength in ultrafine cemented carbide / Cryst. Eng. Comm. 2013. Vol. 15. P. 3305 – 3307.

20. Shawa Leon L., Luob Hong, Zhong Yang. WC-18 wt. % Co with simultaneous improvements in hardness and toughness derived from nanocrystalline powder / Mater. Sci. Engin. A. 2012. Vol. 537. P. 39 – 48.

21. Fang Z. Zak, Wang Xu, Ryu Taegong, Hwang Kyu Sup, Sohn H. Y. Synthesis, sintering, and mechanical properties of nanocrystalline cemented tungsten carbide — A review / Int. J. Refract. Met. Hard Mater. 2009. Vol. 27. P. 288 – 299.

22. Mukhopadhyay A., Basu B. Consolidation-microstructure-property relationships in bulk nanoceramics and ceramic nanocomposites: a review / Int. Mater. Rev. 2007. Vol. 52. N 5. P. 257 – 288.

23. Shatov A. V., Ponomarev S. S., Firstov S. A. Fracture and Strength of Hardmetals at Room Temperature / Compreh. Hard Mater. 2014. Vol. 1. P. 303 – 343.

24. Mukhopadhyay A., Basu B. Consolidation-microstructure-property relationships in bulk nanoceramics and ceramic nanocomposites: a review / Int. Mater. Rev. 2007. Vol. 52. N 5. P. 257 – 288.

25. Dvornik M. I., Mikhailenko E. A. The modeling of the crack propagation process in submicron and nanostructured hard alloys / Nanomech. Sci. Technol. Int. J. 2013. Vol. 4. Issue 3. P. 127 – 210.

26. Armstrong R W., Cazacu O. Indentation fracture mechanics toughness dependence on grain size and crack size: Application to alumina and WC-Co / Int. J. Refract. Met. Hard Mater. 2006. Vol. 24. Issue 2. P. 129 – 134.

27. Nino Akihiro, Tanaka Ayumi, Sugiyama Shigeaki, Taimatsu Hitoshi. Indentation Size Effect for the Hardness of Refractory Carbides / Mater. Trans. 2010. Vol. 51. N 9. P. 1621 – 1626.

28. Lost A., Bigot R. Indentation size effect: reality or artefact? / J. Mater. Sci. 1996. Vol. 31. P. 3573 – 3577.

29. Moshchenok V., Doschechkina I., Lyapin A. Indentation size effect in hardness of materials / Vest. Kharkov. Nats. Avtomob.-Dorozh. Univ. 2008. N 41. P. 71 – 76 [in Russian].

30. Matyunin V. M. The Influence of Scale Effect on the Mechanical Properties of Materials / Zavod. Lab. Diagn. Mater. 2012. Vol. 78. N 2. P. 64 – 68 [in Russian].

31. Spiegler R., Schmadder S., Sigl L. S. Fracture Toughness Evaluation of WC-Co Alloys by Indentation Testing / J. Hard Mater. 1990. Vol. 1. N 3.

32. Rudnayova E., Dusza J., Kupkova M. Comparison of fracture toughness measuring methods applied on silicon nitride ceramics / J. Physique. 1993. Vol. 3. P. C7-1273 – C7-1276.

33. Torres Y., Casellas D., Anglada M., Llanes L. Fracture toughness evolution of hardmetals: influence of testing procedure / Int. J. Refract. Met. Hard Mater. 2001. Vol. 19. P. 27 – 34.

34. Felten F., Schneider A., Sadowski T. Estimation of R-curve in WC/Co cermet by CT test / Int. J. Refract. Met. Hard Mater. 2008. Vol. 26. P. 55 – 60.

35. USSR Inventor’s Certificate, A1G 01 N 3/42. Method of determination of fracture toughness of materials / V. I. Tumanov, L. A. Konyukhova, K. S. Chernyavskiy. N 4049014/25-28; appl. 01.04.86; publ. 07.01.88. Byull. Otkryt. Izobret. 1988. N 1 [in Russian].

36. Yuan Yigao, Zhang Xiaoxiao, Ding Jianjun, Ruan Jun. Measurement of WC grain size in ultrafine grained WC-Co cemented carbides / Appl. Mech. Mater. 2013. Vol. 278 – 280. P. 460 – 463.

37. Shetty D. K., Wright I. G., Mincer P. N., Clauer A. H. Indentation fracture of WC-Co cermets / J. Mater. Sci. 1985. Vol. 20. P. 1873 – 1882.

38. Bonache V., Rayon E., Salvador M. D., Busquets D. Nanoindentation study of WC-12Co hardmetals obtained from nanocrystalline powders: Evaluation of hardness and modulus on individual phases / Mater. Sci. Engin. A. 2010. Vol. 527. P. 2935 – 2941.

39. Engqvist H., Wiklund U. Mapping of mechanical properties of WC-Co using nanoindentation / Tribol. Lett. 2000. Vol. 8. P. 147 – 152.

40. Lee H. C., Gurland J. Hardness and deformation of cemented tungsten carbide / Mater. Sci. Engin. 1978. Vol. 33. Issue 1. P. 125 – 133.

41. Osterstock F., Chermant J.-L. Some Aspects of the Fracture of WC-Co Composites / Sci. Hard Mater. 1983. P. 615 – 629.

42. Godse R., Gurland J. Applicability of the critical strain fracture criterion to WC-Co hard metals / Mater. Sci. Engin. A. 1988. Vol. 105 – 106. Part 2. P. 331 – 336.