Potential application of electron work function in analyzing fracture toughness of materials

doi:10.1016/j.jmst.2017.05.001

Abstract

Abstract:

Fracture toughness determines materials’ resistance to fracture, which is measured often using impact or bending tests. However, it is difficult to evaluate fracture toughness of coatings and small samples. In this article, using white irons as sample materials, we explore a possible approach of using electron work function (EWF) as an indicator in evaluating fracture toughness of hard metallic materials. This parameter is promising for being utilized to analyze toughness of protective coatings and small objects as well as bulk materials. Through comparison with results obtained from impact tests and elastic modulus measurement, effectiveness of this EWF approach is demonstrated.

Key words: Fracture toughness, Elastic modulus, Electron work function

Lu Hao, Ouyang Chenxin, Yan Xianguo, Wang Jian, Hua Guomin, Chung Reinaldo, Li D.Y.. Potential application of electron work function in analyzing fracture toughness of materials[J]. J. Mater. Sci. Technol., 2017, 33(10): 1128-1133.

Figures/Tables 7

Fig. 1. Fracture toughness, decrease in Young’s modulus and EWF change caused by repeated hammering (φ0: EWF before hammering; φf: EWF after hammering; E0: Young’s modulus before hammering; Ef: Young’s modulus after hammering; KIC: fracture toughness).

Table 1 Fracture toughness, changes in Young’s modulus and EWF of samples caused by repeated hammering.

	Fracture toughness (MPa m^1/2)	Changes in relative Young’s modulus, E0-EfE0 (%)	Changes in work function, φ₀-φ_f (eV)
			AFM	Kelvin probe
40-1	19.80	2.43	0.077	0.053
40-2	17.63	2.65	0.079	0.080
40-3	19.63	1.72	0.026	0.034
40-4	19.55	1.59	0.023	0.037
40-5	9.89	7.05	0.112	0.163
40-6	4.67	9.71	0.194	0.250

Table 2 Roughness values of samples before and after repeated hammering.

Sample	Before repeated hammering (nm)	After repeated hammering (nm)
40-1	17.8	19.6
40-2	11.8	21.2
40-3	10.2	12.2
40-4	20.2	24.9
40-5	17.8	25.2
40-6	13.3	13.8

Fig. 2. Fitting curves of relationship between fracture toughness of high-Cr cast irons and changes in their EWF caused by hammering.

Fig. 3. (a) OM images of samples with different carbon concentrations after hammering; both crack density and crack length increase as the carbon concentration increases; (b), (d) and (f) present OM images of 40-1, 40-3 and 40-6 before hammering; (c), (e) and (g) present OM images of 40-1, 40-3 and 40-6 in same regions as those shown in (b), (d) and (f) after hammering.

Fig. 4. Model of a micro-crack, which can be treated as a cluster of vacancies with broken bonds, where the electron density decreases.

Fig. 5. (a) a selected view of sample 40-3 (morphology) with a crack initiated at a carbide caused by repeated hammering, (b) a corresponding EWF map, in which dark regions have lower EWFs and bright regions have higher EWFs, (c) a line profile of EWF in a cracked region of a carbide in 40-3, (d) a line profile of EWF in a cracked region of the matrix in 40-3.

References

[1]	T.L. Anderson, Fracture Mechanics Fundamentals and Applications, third ed.,CRC Press, Boca Raton, 2005.
[2]	W. Callister, D.G. Rethwisch, New York, 2010.
[3]	L. Guo, M. Li, Y. Zhang, F. Ye, J. Mater.Sci.Technol..32(2016) 28-33.
[4]	X. Wang, H. Xiang, X. Sun, J. Liu, F. Hou, Y. Zhou, J. Mater.Sci.Technol..31(2015) 369-374.
[5]	A. Nastic, A. Merati, M. Bielawski, M. Bolduc, O. Fakolujo, M. Nganbe, J.Mater.Sci.Technol..31(2015) 773-783.
[6]	N.D. Lang, W. Kohn, Phys. Rev. B 3 (1971) 1215-1223.
[7]	S. Kamran, K. Chen, L. Chen, Phys. Rev. B 79 (2009) 024106.
[8]	S. Ogata, J. Li, S. Yip, Science 298 (2002) 807-811.
[9]	G.M. Hua, D.Y. Li, Appl. Phys. Lett. 99(2011) 041907.
[10]	H. Lu, G. Hua, D. Li, Appl. Phys. Lett. 103(2013) 261902.
[11]	H. Lu, D. Li, Phys. Status Solidi B 251 (2014) 815-820.
[12]	H. Lu, Z. Liu, X. Yan, D. Li, L. Parent, H. Tian, Sci. Rep. 6(2016) 24366.
[13]	W. Li, D.Y. Li, Appl. Surf. Sci. 240(2005) 388-395.
[14]	A. Mindyuk, Mater. Sci. 7(1974) 608-609.
[15]	V.S. Fomenko, I.A. Podchernyaeva, L.N. Okhremchuk, Sov. Powder Metall. Met.Ceram. 13(1974) 836-842.
[16]	X.F. Wang, T.E. Jones, Y. Wu, Z.P. Lu, S. Halas, T. Durakiewicz, M.E. Eberhart, J.Chem.Phys..141(2014) 024503.
[17]	W. Li, D.Y. Li, Acta Mater. 53(2005) 3871-3878.
[18]	S. Halas, T. Durakiewicz, J. Phys.Condens.Matter..10(1999) 10815.
[19]	E. Case, Y. Kim, J. Mater.Sci..28(1993) 1885-1900.
[20]	N. Laws, J. Brockenbrough, Int. J. Solids Struct. 23(1987) 1247-1268.
[21]	M. Kachanov, Appl. Mech. Rev. 45(1992) 304-335.
[22]	T. Chudoba, M. Griepentrog, A. Dück, D. Schneider, F. Richter, J. Mater.Res..19(2004) 301-314.
[23]	J. Musil, F. Kunc, H. Zeman, H. Poláková, Surf. Coat. Technol. 154(2002)304-313.
[24]	C.C. Chiu, E.D. Case, Mater. Sci. Eng. A 132 (1991) 39-47.
[25]	D.B. Zhu, C.M. Liu, T. Han, Y.D. Liu, H.P. Xie, Appl. Phys. A 120 (2015)1023-1026.
[26]	E. Case, C. Glinka, J. Mater.Sci..19(1984) 2962-2968.
[27]	D.T. Smith, L. Wei, J. Am.Ceram.Soc..78(1995) 1301-1304.
[28]	C. Radin, J. Stat.Phys..131(2008) 567-573.
[29]	H.B. Michaelson, J. Appl.Phys..48(1977) 4729-4733.
[30]	A.N. Obraztsov, A.P. Volkov, A.I. Boronin, S.V. Kosheev, Diamond Relat. Mater.11(2002) 813-818.