Pack boriding of steels is known to possess numerous advantages over conventional techniques like carburizing and nitriding. The combination of high hardness coupled with low co-efficient of friction offered by the diffusion borided layers makes them a promising candidate for combating abrasive, adhesive and erosive wear. However, the boronizing treatment on steels is usually found to result in the formation of a porous, irregular top surface layer and often the borided layer comprises of FeB and Fe2B phases. Of the above, FeB formation is highly undesirable, as it is prone to induce cracking in the coating due to thermal expansion mismatch. While the brittle FeB layer in the boride coating can be eliminated by appropriate post heat treatment or by carefully manipulating the process parameters, porosity and structural irregularity, which play a vital role in tribological performance of the coating, continue to exist in the boride layer. The efficacy of laser post-treatment of the borided layer in overcoming the above problems has been investigated and forms the subject of this paper. A pulsed Nd: YAG laser, capable of delivering an average power of 400W, was utilized for irradiation of the borided layer. Prior to laser treatment, boronizing of En-8 steel samples was carried out by pack-boriding process using an indigenously developed boronizing mixture. The boronized layer was subjected to laser irradiation with varied laser power, under a nitrogen shroud and the laser-treated layers were extensively characterized for surface roughness, phase constitution, microstructure and hardness. Laser glazing resulted in complete densification of the irregular porous top region of the previously boronized layer. An increase in laser power was found to lead to an increase in boride layer depth with accompanying decrease in hardness and porosity. Depending on the laser power employed, distinct microstructures were noted in the treated layer and could be attributed to varying extents of dilution of the boronized layer by Fe from the substrate. Apart from analyzing the influence of laser power on the characteristics of the diffusion borided layer, tribological performance of the laser-treated layers was also evaluated and compared with that of the untreated boride layer. Results of abrasive wear tests indicated substantial improvement in tribological properties and strong dependence on the laser power employed.

1.
A. K.
Sinha
,
ASM Handbook
, Vol.
4
.
ASM International
,
OH, USA
,
1991
; pp.
437
.
2.
R. D. T.
Whittle
,
V. D.
Scott
,
Metals Technology
, Vol.
11
:
1984
; pp.
522
.
3.
W.
Fichtl
,
Materials Engineering
, Vol.
2
:
1981
; pp.
275
.
4.
Vipin
Jain
and
G.
Sundararajan
,
Surface and Coatings Technology
, Vol.
149
:
2002
; pp.
21
.
5.
B.
Chicco
,
W. E.
Borbridge
,
E.
Summerville
,
Surface Engineering
, Vol.
14
(
1
):
1998
,; pp.
25
.
6.
L. L.
Qian
and
G. A.
Stone
,
J. Materials Engineering Performance
, Vol.
4
:
1995
; pp.
59
.
7.
P. A.
Dearnley
and
T.
Bell
,
Surface Engineering
, Vol.
1
:
1985
, pp.
203
.
8.
Ibrahim
Ozbek
and
Cuma
Bindal
,
Surface and Coatings Technology
, Vol.
154
:
2002
; pp.
14
.
9.
J.
Subramanyam
and
K.
Gopinath
,
Wear
, Vol.
95
:
1964
; pp.
287
.
10.
B.
Venkatraman
and
G.
Sundararajan
,
Surface and Coatings Technology
, Vol.
73
:
1995
; pp.
177
.
11.
A.
Bloyce
&
T.
Bhell
,
Laser Treatment of Materials
,
B.L.
Mordike
(Eds),
DGM Informationsgesellschaft-Verlag
,
Germany
(
1987
); pp.
251
.
12.
R.
Ray
,
R.
Hasegawa
,
Solid State Comm
, Vol.
27
:
1978
; pp.
471
.
13.
H.
Burden
,
J. H.
Hunt
,
J. Crystal Growth
, Vol.
22
:
1974
; pp.
328
.
14.
K. G.
Krishna
,
Vipin
Jain
,
B.
Venkatraman
,
K.
Sampath
,
K.
Balasubramanian
and
G.
Sundararajan
, Indian Patent No. 289/MAS/01 April 3,
2001
.
15.
H.
Haferkamp
,
I.
Burmester
and
S.
Czerner
, “
Proc., Europian Conference on laser treatment of materials
”,
B. L.
Mordike
(Eds),
1998
, pp.
16
.
16.
Ke Quan
Zheng
and
Si Yu
Zhang
,
Materials Letters
, Vol.
10/4
and
5
: Nov,
1990
, pp.
195
.
17.
R. V.
Subba Rao
,
P.
Parameswaran
,
R. K.
Dayal
and
R. K.
Sole
,
Proc., of Intnl. Symposium on Materials Aging and Life Management
,.
Baldev
Raj
,
K. B. S.
Rao
,
T.
Jayakumar
and
R. K.
Dayal
(Eds), Oct:
2002
, pp.
502
.
18.
M.
Shariff
,
G.
Sundararjan
and
S. V.
Joshi
,
Proc. Surface Modifications Technologies XIII
,
T. S.
Sudarshan
,
K. A.
Khor
and
M.
Jeandin
(Eds),
1999
, pp.
135
.
19.
M.
Tayal
and
K.
Mukherjee
,
J. of Materials Science
, Vol.
29
:
1994
; pp.
5699
.
20.
K.
Komvopoulus
and
K.
Nagarathnam
,
J. of Engineering Materials & Technology
, Vol.
112
:
1990
; pp.
131
.
21.
S. V.
Joshi
,
G.
Thawari
,
L.
Srinivas Kumar
,
D.
Sen
and
G.
Sundararajan
, “
Proce. Of International Thermal Spray Conference
,
C. C.
Berndt
,
K. A.
Khor
and
E. F.
Lugscheider
(Eds),
ASM International
,
Ohio, USA
:
2001
, pp.
583
.
22.
Mordike
B. L.
and
Sivakumar
R
,
Surface Engineering
, Vol.
4
(
2
):
1988
; pp.
127
.
23.
E.
Hornbogen
and
S.
Staniek
,
Z.
Metallkde
, Vol.
79
(
H-6
):
1988
; pp.
375
.
24.
J.
Senthil Selvan
,
K.
Subramanian
,
A. K.
Nath
,
H.
Kumar
,
C.
Ramchandra
and
S. P.
Ravindranathan
,
Materials and Engineering
, Vol.
A260
:
1999
; pp.
178
.
25.
H.E.
Cline
&
T.R.
Anthony
,
J. of Applied Physics
, Vol.
48
(
9
):
1977
; pp.
389
.
26.
C.
Courtney
and
W. M.
Steen
,
1978
,
Proc.,of Int. Conference on Advances in Surface Coating Technology
,
British Welding Institute
,
England
, pp.
219
.
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