Journal of Materials Science

, Volume 45, Issue 23, pp 6540–6555

Fracture toughness modification by using a fibre laser surface treatment of a silicon nitride engineering ceramic

Authors

    • Loughborough University, Wolfson School of Mechanical and Manufacturing Engineering
  • J. Lawrence
    • Loughborough University, Wolfson School of Mechanical and Manufacturing Engineering
Article

DOI: 10.1007/s10853-010-4743-6

Cite this article as:
Shukla, P.P. & Lawrence, J. J Mater Sci (2010) 45: 6540. doi:10.1007/s10853-010-4743-6

Abstract

Surface treatment of a silicon nitride (Si3N4) engineering ceramic with fibre laser radiation was conducted to identify changes in the fracture toughness as measured by K1c. A Vickers macro-hardness indentation method was adopted to determine the K1c of the Si3N4 before and after fibre laser surface treatment. Optical and a scanning electron microscopy (SEM), a co-ordinate measuring machine and a focus variation technique were used to observe and measure the dimensions of the Vickers indentation, the resulting crack lengths, as well as the crack geometry within the as-received and fibre laser-treated Si3N4. Thereafter, computational and analytical methods were employed to determine the K1c using various empirical equations. The equation K1c = 0.016 (E/Hv)1/2 (P/c3/2) produced most accurate results in generating K1c values within the range from 4 to 6 MPa m1/2. From this it was found that the indentation load, hardness, along with the resulting crack lengths in particular, were the most influential parameters within the K1c equation used. An increase in the near surface hardness of 4% was found with the Si3N4 in comparison with the as-received surface, which meant that the fibre laser-treated surface of the Si3N4 became harder and more brittle, indicating that the surface was more prone to cracking after the fibre laser treatment. Yet, the resulting crack lengths from the Vickers indentation tests were reduced by 37% for the Si3N4 which in turn led to increase in the K1c by 47% in comparison with the as-received surface. It is postulated that the fibre laser treatment induced a compressive stress layer by gaining an increase in the dislocation movement during elevated temperatures from the fibre laser surface processing. This inherently increased the compressive stress within the Si3N4 and minimized the crack propagation during the Vickers indentation test, which led to the fibre laser-radiated surface of the Si3N4 engineering ceramic to have more resistance to crack propagation.

List of symbols

Kc

Plane stress fracture toughness

K1c

Fracture Toughness

CO2

Carbon dioxide

CW

Continuous wave

Hv

Hardness

E

Young’s modulus

N

Newton’s

c

Average flaw size

P

Load (kg)

Pc

Load impact

Ic

Interior cracks

m min−1

Metre per minute

HIP

Hot isostatic pressed

CIP

Cold isostatic pressed

O2

Oxygen

Si3N4

Silicon nitride

ZrO2

Zirconia oxide

Al2O3

Alumina

Sic

Silicon carbide

MgO

Magnesia oxide

PSZ

Partially stabilized zirconia

SiO2

Silicon dioxide

kg

Kilo gram

MPa

Mega pascal

GPa

Giga pascal

Μm

Micro metre

M

Meters

m2

Meter cubed

mm

Millimetres

L

Litres

CMM

Co-ordinate measuring machine

δ

Delta

β

Beta

°C

Degrees centigrade

NC

Numerical control

θ

Theta

D

Average diagonal size

YSiAlON

Sailon

Nd:YAG

Neodinium Yttrium Aluminium Garnet

Copyright information

© Springer Science+Business Media, LLC 2010