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Sliding wear resistance of tool steel coated with electroless Ni-P and cathodic arc plasma TiN
Surface and Coatings Technology, 53 (1992) 87—92
87
Sliding wear resistance of tool steel coated with electroless Ni—P and cathodic arc plasma TiN J. L. He and M. H. Hon Department of Materials Engineering, National Cheng Kung University, Tainan (Taiwan) (Received January 17, 1992: accepted February 28, 1992)
Abstract A wear-resistant hybrid-coating technique combining electroless Ni—P plating and cathodic arc plasma TiN deposition was used to coat a composite layer on SKD1 I tool steel. The wear rate (based on surface profile and weight loss) and friction coefficient were assessed using a Felex 6 wear tester; also, the washer-on-disk method was used to evaluate the sliding wear resistance. Experimental results and analysis showed that such a hybrid coating could provide a better load-carrying capacity than a single TiN layer. A reduction in cracking and spalling of the hybrid-coating layers was observed during wear.
1. Introduction Titanium nitride (TiN) coated by various reactive ionplating methods has been widely used to promote tool performance and to reduce the thrust force [l—9]. In some cases, cracking and spalling of the TiN layer may accelerate the wear rate of tools under more severe conditions. For instance, a new laboratory wear test was used by Hedenqvist et a!. [10] to investigate the influence of TiN coating on the wear resistance of high speed steel tools. They found that the TiN coating was removed rapidly by interfacial spalling when sliding against austenitic steel. The TiN layer was cracked and depressed into the substrate and a wavy wear topography was formed at a high sliding speed. Hedenqvist et al. [11] also proposed that cracking and plucking mechanisms dominated the deterioration process and no continuous wear of the TiN coating was observed in high temperature sliding wear tests. Page and Knight [12] indicated that factors affecting the tribological behaviour of TiN and TiC coatings included the scale effect of the surface deformation zone, residual stress in the coating and the yield deformation and flow properties of the substrate. A metallic titanium interlayer was introduced [13] on the substrate before TiN coating to modify the interfacial flow distribution and to strengthen the coating—substrate adhesion as conducted by Rickerby et a!. [14]. However, the titanium interlayer might reduce the apparent hardness of the coated specimen as pointed out by Chen and Duh [15] and consequently the load-carrying capacity. Therefore they precoated Ni—P as an interlayer on mild steel and found a promotion of surface hardness and a strengthening of the adhesion between coating and sub-
0257—89729285.00
_
ROTARY ~IPL1LE (WITH DRIVE PINS)
~—
ROTARY SPECIMEN HOLDER
WASHER (COUNTER MATERIAL)
TEST SPECIMEN
‘—S
STATIONARY SPECIMEN HOLDER
LOAD Fig. 1. Thrust washer-on-disk test specimen arrangement.
strate. Reichel et al. [16] have demonstrated an improvement in corrosion resistance by introducing electroless Ni—P plating and cathodic arc plasma (CAP) TiN coating on high speed tool steel. Dennis and Sagoo [17] compared the wear behaviour of several duplex-coated tool steels using the pin-on-disk method. A specimen coated with electroless Ni—P and physical vapour deposition (PVD) TiN was the most wear resistant in tests with a load of 4 kgf on the pin. These investigations on
y~1992— Elsevier Sequoia. All rights reserved
55
.1. 1.. lie. \l. 11. lion
Wear reo000ec
hybrid coatings indicated that there was a possibility of applying them on tool steel. Thus a quantitative description of wear resistance and a direct comparison between single-TiN-coated and hybrid-coated specimens should he investigated. In this study electroless Ni P was plated on SKD! I tool steel, as an interlayer which was expected to increase the load-carrying capacity. then followed by a CAP TiN deposition. The sliding wear resistance of such a hybridcoated SKDI I tool was then investigated,
f (ac//cd /0)1 0cc!
then ultrasonically cleaned in a hydrochloric acid solution. Electroless plating was carried out in a beaker which was heated by a stirrer hot plate. Nickora. produced by the Schering company, was used as the Ni P-plating solution. The plating parameters used in this study were as follows: plating temperature 90 C. pH 4.9. coating thickness 5 p.m. CAP-TiN deposition was carried out in a Hauzer arc ion-plating system. Before TiN coating, the electrolessplated specimen was placed in the coating chamber. heated to 400 C by an argon discharge and held for 60 mm to stabilize and harden the Ni P layer, then cleaned by sputtering for 10 mm. Once started, nitrogen gas was fed into the coating chamber to keep the base pressure at 8 >< JO ~mbar. Evaporators were initiated. The cathode voltage and current were maintained at 18 V and 80 A respectively. The substrate bias voltage was maintained at —100 V. The coating time was 40 mm and a 2 p.m TiN film was obtained. -
2. Experimental details SK DII tool steel specimens were cut and shaped to form a disk for sliding wear tests as illustrated in Fig. I. These samples were heat treated, ground and then surface polished by 0.3 p.m alumina powder. Before electroless plating, the specimens were degreased and
SUBSTRATE
2 ,~Jm
(a)
~
~
~~SUBSTRATE Ic
(
~-~cciI
_
-___
20 ,um
hi I
__
iial inicrographs of (a) TiN layer coating and (hi hy hrid layer coating.
4
J. L. He, M. H. Hon / Wear resistance of coated tool steel
‘0
89
25
~2O —
CPZZWZZ
~15
Z
__ I
25
F: ~ I
31
37
43
I
I
I
c’ I
49 55 61 67 Spectral angle
73
79
Fig. 3. XRD patterns of (a) hybrid-coated. (b) TiN-coated and (c) uncoated SKDI I specimens. Peaks marked “5” originate from the substrate. TABLE 1. Weight loss and wear resistance ratio, defined by inversion of weight loss of specimen, after sliding for 750 m
___________________________________________ Specimen Weight loss (l0~g) Wear resistance ratio ________________________________ Uncoated SKDII 243 Ni—P plated SKDI 1 267 TiN-coated SKDI 1 42 Hybrid-coated SKDI 1 9
E
0
200 180 160 140 120 100 80 60 40 20
4à0 8ö0 120d i600 SUDING DISTANCE (m)
85
1.0 0.9 5.9 27.0
Fig. 5. Wear rate of uncoated, TiN-coated and hybrid-coated SKDI I specimens.
200
E
180 160
(a) ~
(b) 140 ~ 120 (c) ~ 100 80 ~
60 20
(b) ~ -
(c)
I
(9.o
(a)
______
-
-(d) ~
I
I
I
0.5 1.0 1.5 2.0 2.5 PROFILE SCANNING LENGTH (mm)
19.0
0.5 1.0 1.5 2.0 2.5 PROFILE SCANNING LENGTH (mm) Fig. 6. Wear scar profiles of TiN-coated SKDI I afler sliding for (a) 230. (b) 470, (c) 750 and (d) 1500 m. was measured by a digital balance to four-decimal-point precision and the wear scar profile was measured vertically along the sliding wear direction by a profilometer. The metallography of the wear scar was observed by scanning electron microscopy (SEM). The microstructure of the deposited films was characterized by X-ray diffraction (XRD) and SEM.
Fig. 4. Wear scar profiles of (a) uncoated, (b) Ni—P-plated, (c) TiNcoated and (d) hybrid-coated SKDI I specimens after sliding for 750 m.
3. Results and discussion
Sliding wear tests using the washer-on-disk method described in ASTM D3702—78 were conducted in a Felex 6 multifunction wear tester. For comparison, specimens with and without Ni—P plating were both CAP-TiN coated. The disk specimen and washer were installed as shown in Fig. 1. The washer as counter material was made of S45C medium carbon steel. The wear test conditions chosen were as follows: load 22.7 kgf, drive speed 500 rev min ambient ternperature. After the wear test the weight loss of the disk specimen
Figures 2(a) and 2(b) show single-TiN-deposited and hybrid-coated layers on SKD1 I respectively. Both the TiN coatings have columnar structures with macropartides embedded in them. XRD patterns indicate that both coatings have a (Ill) texture as shown in Fig. 3. The diffraction pattern of the hybrid-coated specimen appeared to have some weak and very weak peaks which the single-TiN-coated one did not have. These peaks could come from crystallization of the Ni—P layer during subsequent preheating and the TiN-coating procedure. Except for this, there is almost no difference between
~,
9(1
J. I.. Ih, M. Ii. 1-ion
Weai rc,s-isIance of coated too! s/er’!
SLIDING DIRECTION
____
_
-
:HI:NEDTYTR
400pm
2pm
Fig. 7. Thinned TiN layer located in centre of wear scar.
these two TiN layers observed in the XRD patterns. In such a case, what really improved the wear resistance of the hybrid-coated specimen is the contribution from the hybrid coating “composite” rather than the TiN coating alone. For the purpose of direct comparison of wear resistance, the wear scar profile and weight loss of specimens after sliding for 750 m were measured (Table I, Fig. 4). It is obvious that the single-Ni-- P-plated specimen did not perform well in the sliding wear resistance test. Although the high hardness and strong adhesion of the heat-treated Ni P layer are well known, Ni--P is not as chemically inert as TiN and some sort of chemical wear might have occurred during the sliding wear test. Thus
___
________ _____
20 pm Fig. 5. Cracked TiN layer near wear sear edge.
the wear resistance is not much improved compared with that obtained for uncoated SKDI I. The CAP-TiNcoated specimen showed a progressive improvement in wear resistance compared with the uncoated specimen. The weight loss is one-sixth that of uncoated SKDI I for the same sliding distance in the wear test (Table I). This means that the lifetime of CAP-TiN-coated SKDII is six times greater than for uncoated SKDI I. This result falls into the common range of lifetimes of TiN-coated tools. The hybrid-coated specimen appeared to have a higher wear resistance than the single-CAP-TiN-coated specimen. Only a slight volume loss and weight loss could be measured. The weight loss of the hybrid-coated specimen was only one-quarter that of the single-CAP-
SLIDING DIRECTION
J. L. He, M. H. Hon / Wear resistance of coated tool steel
91
SLIDING DIRECTION
______
E-. 120
~
: 80 .(b)
PROFILE
~
SCANNING LENGTH
(mm)
Fig. II. Attachment of spalled TiN film on Ni—P-plated SKDI I, forming a wavy feature.
Fig. 9. Wear scar profiles of hybrid-coated SKDI I after sliding for (a) 750 and (b) lSOOm.
1.0 0 HYBRID COATING * CAP TIN COATING
______________
____
D~EC1~ON
~
0.0 Fig.
—
60 )Jm Fig. 10.
C
Wear scar of hybrid-coated SKDI I after
iào
260360
~TA~
(6r
760
8~0
12. Friction coefficient of TiN-coated and hybrid-coated SKDI 1
specimens.
sliding for
750 m.
TiN-coated specimen. This indicated that a factor-of-24 lifetime increase could be achieved for the hybrid-coated specimen compared to the uncoated SKDI I. A comparison of weight loss dependence on sliding distance for the uncoated, single-TiN-coated and hybrid-coated specimens is shown in Fig. 5. The hybrid-coated specimen possessed a superior wear resistance to the single-TiNcoated specimen up to a sliding distance of 1500 m. Figure 6 shows the wear scar profiles of a single-TiNcoated specimen for different sliding distances. There was only local wear damage for sliding within 750 m. A large area of volume loss could be observed after sliding for 1500 m. Major wear damage of the TiN layer was in the form of cracking and interfacial spalling accompanied by adhesive wear. The adhesive wear caused a continuous reduction in TiN film thickness, which was observed on the remaining film located in the centre of the scar area as shown in Fig. 7. The TiN film was thinned from an original 1.8 p.m to 1.2 p.m after sliding for 1500 m. Cracking of the TiN layer was observed near the edge of wear scar as shown in Fig. 8. These phenomena could be due to the low load-carrying capacity of the coating—substrate composite. Figure 9
shows the wear scar profiles of the hybrid-coated specimen after sliding for 750 and 1500 m. Only a local area of volume loss existed even after sliding for 1500 m. Figure 10 shows the wear scar of the hybrid-coated specimen after sliding for 750 m. Spalled TiN film was still attached tightly in some regions and formed a wavy feature as shown in Fig. 11. Thus it created a rougher surface and a higher friction coefficient in the initial wearing stage in comparison with the single-TiN-coated specimen (Fig. 12). These spalled films were subsequently embedded in the Ni—P layer and still contributed to the wear resistance without causing damage to the substrate. This is unlike the wear feature of the single TiN coating; thus a significant reduction in wear rate could be achieved. These embedded films were continuously worn by adhesive wear and gradually diminished. The remaining pieces embedded in the Ni—P layer were observed in some wear scar regions after sliding for 1500 m as seen in Fig. 13. To sum up, the contribution of the Ni—P layer to the wear resistance was in providing a physically medium hard interlayer which acted as a load-bearing support to the top TiN layer or even spalled TiN pieces as modelled in Fig. 14. This Ni—P interlayer might pro-
.1 /
i/c
‘ii 11. Il,c,i
till/I
rc’sIcIcIIIc-e ‘f cocIIe,/ l,s’! sic’,!
SLIDING DIRECTION
~c5~
40,um Hg. 13. Remaining fiN pieces emhedded in Ni
P laker cuter slidIng (or I ~IIl) Il/.
SLIDING DIRECTION
SLIDING DIRECTION
Acknowledgments
~WAVING
~
CR~CKIN~ALLING
T(NLTHINNING -
~
~ THINMNG
1
suB~
The authors wish to thank the Metal Industries Development Centre for providing the CAP facility and Professor Lin who provided the Felex wear tester. References
,
1-ig. 14. Schema/ic diagi am oi major a ear eat UI CS a) and I h) hrhrid—coatcd SK DII specimens
(.1) TiN coaled
I S. Rodeos :01(1 H. Veltrop. Surf. foal. Jeeli,io! .H_/ (19571 63 2 ‘s. M llrawa. Heal I real - -th’r. - 2 ((956) 49. 3 W. I). Sproul and R. Rothstein. i//ill Solo! I-i/nI), 126 1955i 257 4 55. t). M iini. 1). I—Iofman n and K - I-I art ig. ill/I So/ic! I i/Ill.) -
(I
1952) 79.
gressively improve the wear resistance of TiN—coated tools as well as other hard—coated components in an economical way.
~ M. lohler, ~IIIIsIof/e (er. PIci.si.. ‘) ((959) 5. 6 H. .1. Michael. SlIr!. (‘cull. Technol., 29 (19S6) 221 7 I. L. (‘hurch, Macf. .5/er.. 44)5) (1955)32. 5 .1. Kusrnierz, bc,!. Pr,, 1!.. 55)7) (Octoher) (1959) (~5 ‘1 J. Alesander, Fahrlc-aI,cr. /9 (2(11959/ 24. 1) P. Hendenqvisl. M. Olsson and S. Sodcrherg..Si~r[
4. Conclusions I
Significant improvement in the sliding wear resistance of SKDI I tool steel was obtained by a hybrid-coating technique combining electroless Ni P plating and CAP TiN coating. The Ni P layer provided a better loadcarrying capacity for hybrid-coated specimens than that of specimens coated by only a single TiN layer. A reduction in cracking and spalling of the hybrid-coating layers was observed during wear; hence improved wear resistance could be obtained.
LIly.
cOld S. .I:Icohson, Surf. (oar. lecSInol.. 41(1991)1243. P pa. aid I ( Kni~ht StcIf ( ‘II icc 111101
I— I I
3
4(1 (959)
3 H. Malthes, F. Broszcit and K. II. Kloos. Surf ( ocil. icc
-is
-
5 (21
(1959) 141. 1’, Hendenqrisl. M. Olwon. P. WaIlen. A. Kassman. S. Hogmark
111101
44(1990) 721.
(4 D. S. Rlckerh5, S. J. Bull. I. Roherlson and A. Hcndr~ Surf. (0,0. -
/c’I1III0L,
4/0996163.
.
- -
Ia ‘s I. C hen and J. Ci. Duh. Surf. (cult. lee/mo!., .1,5 (1991) 163. 16 K Reichel. W Brandl, M. Mack. H. H. 1-Jrlherger md H Kleini, (~,I!Icl1I0lt’c/i,iik,
Si (2 (1991)1 426.
17 .1. K. Dennis and K. S. Sagoo. tie!. I-orish.. 59(61 (jcmne( (1991) III -
87
Sliding wear resistance of tool steel coated with electroless Ni—P and cathodic arc plasma TiN J. L. He and M. H. Hon Department of Materials Engineering, National Cheng Kung University, Tainan (Taiwan) (Received January 17, 1992: accepted February 28, 1992)
Abstract A wear-resistant hybrid-coating technique combining electroless Ni—P plating and cathodic arc plasma TiN deposition was used to coat a composite layer on SKD1 I tool steel. The wear rate (based on surface profile and weight loss) and friction coefficient were assessed using a Felex 6 wear tester; also, the washer-on-disk method was used to evaluate the sliding wear resistance. Experimental results and analysis showed that such a hybrid coating could provide a better load-carrying capacity than a single TiN layer. A reduction in cracking and spalling of the hybrid-coating layers was observed during wear.
1. Introduction Titanium nitride (TiN) coated by various reactive ionplating methods has been widely used to promote tool performance and to reduce the thrust force [l—9]. In some cases, cracking and spalling of the TiN layer may accelerate the wear rate of tools under more severe conditions. For instance, a new laboratory wear test was used by Hedenqvist et a!. [10] to investigate the influence of TiN coating on the wear resistance of high speed steel tools. They found that the TiN coating was removed rapidly by interfacial spalling when sliding against austenitic steel. The TiN layer was cracked and depressed into the substrate and a wavy wear topography was formed at a high sliding speed. Hedenqvist et al. [11] also proposed that cracking and plucking mechanisms dominated the deterioration process and no continuous wear of the TiN coating was observed in high temperature sliding wear tests. Page and Knight [12] indicated that factors affecting the tribological behaviour of TiN and TiC coatings included the scale effect of the surface deformation zone, residual stress in the coating and the yield deformation and flow properties of the substrate. A metallic titanium interlayer was introduced [13] on the substrate before TiN coating to modify the interfacial flow distribution and to strengthen the coating—substrate adhesion as conducted by Rickerby et a!. [14]. However, the titanium interlayer might reduce the apparent hardness of the coated specimen as pointed out by Chen and Duh [15] and consequently the load-carrying capacity. Therefore they precoated Ni—P as an interlayer on mild steel and found a promotion of surface hardness and a strengthening of the adhesion between coating and sub-
0257—89729285.00
_
ROTARY ~IPL1LE (WITH DRIVE PINS)
~—
ROTARY SPECIMEN HOLDER
WASHER (COUNTER MATERIAL)
TEST SPECIMEN
‘—S
STATIONARY SPECIMEN HOLDER
LOAD Fig. 1. Thrust washer-on-disk test specimen arrangement.
strate. Reichel et al. [16] have demonstrated an improvement in corrosion resistance by introducing electroless Ni—P plating and cathodic arc plasma (CAP) TiN coating on high speed tool steel. Dennis and Sagoo [17] compared the wear behaviour of several duplex-coated tool steels using the pin-on-disk method. A specimen coated with electroless Ni—P and physical vapour deposition (PVD) TiN was the most wear resistant in tests with a load of 4 kgf on the pin. These investigations on
y~1992— Elsevier Sequoia. All rights reserved
55
.1. 1.. lie. \l. 11. lion
Wear reo000ec
hybrid coatings indicated that there was a possibility of applying them on tool steel. Thus a quantitative description of wear resistance and a direct comparison between single-TiN-coated and hybrid-coated specimens should he investigated. In this study electroless Ni P was plated on SKD! I tool steel, as an interlayer which was expected to increase the load-carrying capacity. then followed by a CAP TiN deposition. The sliding wear resistance of such a hybridcoated SKDI I tool was then investigated,
f (ac//cd /0)1 0cc!
then ultrasonically cleaned in a hydrochloric acid solution. Electroless plating was carried out in a beaker which was heated by a stirrer hot plate. Nickora. produced by the Schering company, was used as the Ni P-plating solution. The plating parameters used in this study were as follows: plating temperature 90 C. pH 4.9. coating thickness 5 p.m. CAP-TiN deposition was carried out in a Hauzer arc ion-plating system. Before TiN coating, the electrolessplated specimen was placed in the coating chamber. heated to 400 C by an argon discharge and held for 60 mm to stabilize and harden the Ni P layer, then cleaned by sputtering for 10 mm. Once started, nitrogen gas was fed into the coating chamber to keep the base pressure at 8 >< JO ~mbar. Evaporators were initiated. The cathode voltage and current were maintained at 18 V and 80 A respectively. The substrate bias voltage was maintained at —100 V. The coating time was 40 mm and a 2 p.m TiN film was obtained. -
2. Experimental details SK DII tool steel specimens were cut and shaped to form a disk for sliding wear tests as illustrated in Fig. I. These samples were heat treated, ground and then surface polished by 0.3 p.m alumina powder. Before electroless plating, the specimens were degreased and
SUBSTRATE
2 ,~Jm
(a)
~
~
~~SUBSTRATE Ic
(
~-~cciI
_
-___
20 ,um
hi I
__
iial inicrographs of (a) TiN layer coating and (hi hy hrid layer coating.
4
J. L. He, M. H. Hon / Wear resistance of coated tool steel
‘0
89
25
~2O —
CPZZWZZ
~15
Z
__ I
25
F: ~ I
31
37
43
I
I
I
c’ I
49 55 61 67 Spectral angle
73
79
Fig. 3. XRD patterns of (a) hybrid-coated. (b) TiN-coated and (c) uncoated SKDI I specimens. Peaks marked “5” originate from the substrate. TABLE 1. Weight loss and wear resistance ratio, defined by inversion of weight loss of specimen, after sliding for 750 m
___________________________________________ Specimen Weight loss (l0~g) Wear resistance ratio ________________________________ Uncoated SKDII 243 Ni—P plated SKDI 1 267 TiN-coated SKDI 1 42 Hybrid-coated SKDI 1 9
E
0
200 180 160 140 120 100 80 60 40 20
4à0 8ö0 120d i600 SUDING DISTANCE (m)
85
1.0 0.9 5.9 27.0
Fig. 5. Wear rate of uncoated, TiN-coated and hybrid-coated SKDI I specimens.
200
E
180 160
(a) ~
(b) 140 ~ 120 (c) ~ 100 80 ~
60 20
(b) ~ -
(c)
I
(9.o
(a)
______
-
-(d) ~
I
I
I
0.5 1.0 1.5 2.0 2.5 PROFILE SCANNING LENGTH (mm)
19.0
0.5 1.0 1.5 2.0 2.5 PROFILE SCANNING LENGTH (mm) Fig. 6. Wear scar profiles of TiN-coated SKDI I afler sliding for (a) 230. (b) 470, (c) 750 and (d) 1500 m. was measured by a digital balance to four-decimal-point precision and the wear scar profile was measured vertically along the sliding wear direction by a profilometer. The metallography of the wear scar was observed by scanning electron microscopy (SEM). The microstructure of the deposited films was characterized by X-ray diffraction (XRD) and SEM.
Fig. 4. Wear scar profiles of (a) uncoated, (b) Ni—P-plated, (c) TiNcoated and (d) hybrid-coated SKDI I specimens after sliding for 750 m.
3. Results and discussion
Sliding wear tests using the washer-on-disk method described in ASTM D3702—78 were conducted in a Felex 6 multifunction wear tester. For comparison, specimens with and without Ni—P plating were both CAP-TiN coated. The disk specimen and washer were installed as shown in Fig. 1. The washer as counter material was made of S45C medium carbon steel. The wear test conditions chosen were as follows: load 22.7 kgf, drive speed 500 rev min ambient ternperature. After the wear test the weight loss of the disk specimen
Figures 2(a) and 2(b) show single-TiN-deposited and hybrid-coated layers on SKD1 I respectively. Both the TiN coatings have columnar structures with macropartides embedded in them. XRD patterns indicate that both coatings have a (Ill) texture as shown in Fig. 3. The diffraction pattern of the hybrid-coated specimen appeared to have some weak and very weak peaks which the single-TiN-coated one did not have. These peaks could come from crystallization of the Ni—P layer during subsequent preheating and the TiN-coating procedure. Except for this, there is almost no difference between
~,
9(1
J. I.. Ih, M. Ii. 1-ion
Weai rc,s-isIance of coated too! s/er’!
SLIDING DIRECTION
____
_
-
:HI:NEDTYTR
400pm
2pm
Fig. 7. Thinned TiN layer located in centre of wear scar.
these two TiN layers observed in the XRD patterns. In such a case, what really improved the wear resistance of the hybrid-coated specimen is the contribution from the hybrid coating “composite” rather than the TiN coating alone. For the purpose of direct comparison of wear resistance, the wear scar profile and weight loss of specimens after sliding for 750 m were measured (Table I, Fig. 4). It is obvious that the single-Ni-- P-plated specimen did not perform well in the sliding wear resistance test. Although the high hardness and strong adhesion of the heat-treated Ni P layer are well known, Ni--P is not as chemically inert as TiN and some sort of chemical wear might have occurred during the sliding wear test. Thus
___
________ _____
20 pm Fig. 5. Cracked TiN layer near wear sear edge.
the wear resistance is not much improved compared with that obtained for uncoated SKDI I. The CAP-TiNcoated specimen showed a progressive improvement in wear resistance compared with the uncoated specimen. The weight loss is one-sixth that of uncoated SKDI I for the same sliding distance in the wear test (Table I). This means that the lifetime of CAP-TiN-coated SKDII is six times greater than for uncoated SKDI I. This result falls into the common range of lifetimes of TiN-coated tools. The hybrid-coated specimen appeared to have a higher wear resistance than the single-CAP-TiN-coated specimen. Only a slight volume loss and weight loss could be measured. The weight loss of the hybrid-coated specimen was only one-quarter that of the single-CAP-
SLIDING DIRECTION
J. L. He, M. H. Hon / Wear resistance of coated tool steel
91
SLIDING DIRECTION
______
E-. 120
~
: 80 .(b)
PROFILE
~
SCANNING LENGTH
(mm)
Fig. II. Attachment of spalled TiN film on Ni—P-plated SKDI I, forming a wavy feature.
Fig. 9. Wear scar profiles of hybrid-coated SKDI I after sliding for (a) 750 and (b) lSOOm.
1.0 0 HYBRID COATING * CAP TIN COATING
______________
____
D~EC1~ON
~
0.0 Fig.
—
60 )Jm Fig. 10.
C
Wear scar of hybrid-coated SKDI I after
iào
260360
~TA~
(6r
760
8~0
12. Friction coefficient of TiN-coated and hybrid-coated SKDI 1
specimens.
sliding for
750 m.
TiN-coated specimen. This indicated that a factor-of-24 lifetime increase could be achieved for the hybrid-coated specimen compared to the uncoated SKDI I. A comparison of weight loss dependence on sliding distance for the uncoated, single-TiN-coated and hybrid-coated specimens is shown in Fig. 5. The hybrid-coated specimen possessed a superior wear resistance to the single-TiNcoated specimen up to a sliding distance of 1500 m. Figure 6 shows the wear scar profiles of a single-TiNcoated specimen for different sliding distances. There was only local wear damage for sliding within 750 m. A large area of volume loss could be observed after sliding for 1500 m. Major wear damage of the TiN layer was in the form of cracking and interfacial spalling accompanied by adhesive wear. The adhesive wear caused a continuous reduction in TiN film thickness, which was observed on the remaining film located in the centre of the scar area as shown in Fig. 7. The TiN film was thinned from an original 1.8 p.m to 1.2 p.m after sliding for 1500 m. Cracking of the TiN layer was observed near the edge of wear scar as shown in Fig. 8. These phenomena could be due to the low load-carrying capacity of the coating—substrate composite. Figure 9
shows the wear scar profiles of the hybrid-coated specimen after sliding for 750 and 1500 m. Only a local area of volume loss existed even after sliding for 1500 m. Figure 10 shows the wear scar of the hybrid-coated specimen after sliding for 750 m. Spalled TiN film was still attached tightly in some regions and formed a wavy feature as shown in Fig. 11. Thus it created a rougher surface and a higher friction coefficient in the initial wearing stage in comparison with the single-TiN-coated specimen (Fig. 12). These spalled films were subsequently embedded in the Ni—P layer and still contributed to the wear resistance without causing damage to the substrate. This is unlike the wear feature of the single TiN coating; thus a significant reduction in wear rate could be achieved. These embedded films were continuously worn by adhesive wear and gradually diminished. The remaining pieces embedded in the Ni—P layer were observed in some wear scar regions after sliding for 1500 m as seen in Fig. 13. To sum up, the contribution of the Ni—P layer to the wear resistance was in providing a physically medium hard interlayer which acted as a load-bearing support to the top TiN layer or even spalled TiN pieces as modelled in Fig. 14. This Ni—P interlayer might pro-
.1 /
i/c
‘ii 11. Il,c,i
till/I
rc’sIcIcIIIc-e ‘f cocIIe,/ l,s’! sic’,!
SLIDING DIRECTION
~c5~
40,um Hg. 13. Remaining fiN pieces emhedded in Ni
P laker cuter slidIng (or I ~IIl) Il/.
SLIDING DIRECTION
SLIDING DIRECTION
Acknowledgments
~WAVING
~
CR~CKIN~ALLING
T(NLTHINNING -
~
~ THINMNG
1
suB~
The authors wish to thank the Metal Industries Development Centre for providing the CAP facility and Professor Lin who provided the Felex wear tester. References
,
1-ig. 14. Schema/ic diagi am oi major a ear eat UI CS a) and I h) hrhrid—coatcd SK DII specimens
(.1) TiN coaled
I S. Rodeos :01(1 H. Veltrop. Surf. foal. Jeeli,io! .H_/ (19571 63 2 ‘s. M llrawa. Heal I real - -th’r. - 2 ((956) 49. 3 W. I). Sproul and R. Rothstein. i//ill Solo! I-i/nI), 126 1955i 257 4 55. t). M iini. 1). I—Iofman n and K - I-I art ig. ill/I So/ic! I i/Ill.) -
(I
1952) 79.
gressively improve the wear resistance of TiN—coated tools as well as other hard—coated components in an economical way.
~ M. lohler, ~IIIIsIof/e (er. PIci.si.. ‘) ((959) 5. 6 H. .1. Michael. SlIr!. (‘cull. Technol., 29 (19S6) 221 7 I. L. (‘hurch, Macf. .5/er.. 44)5) (1955)32. 5 .1. Kusrnierz, bc,!. Pr,, 1!.. 55)7) (Octoher) (1959) (~5 ‘1 J. Alesander, Fahrlc-aI,cr. /9 (2(11959/ 24. 1) P. Hendenqvisl. M. Olsson and S. Sodcrherg..Si~r[
4. Conclusions I
Significant improvement in the sliding wear resistance of SKDI I tool steel was obtained by a hybrid-coating technique combining electroless Ni P plating and CAP TiN coating. The Ni P layer provided a better loadcarrying capacity for hybrid-coated specimens than that of specimens coated by only a single TiN layer. A reduction in cracking and spalling of the hybrid-coating layers was observed during wear; hence improved wear resistance could be obtained.
LIly.
cOld S. .I:Icohson, Surf. (oar. lecSInol.. 41(1991)1243. P pa. aid I ( Kni~ht StcIf ( ‘II icc 111101
I— I I
3
4(1 (959)
3 H. Malthes, F. Broszcit and K. II. Kloos. Surf ( ocil. icc
-is
-
5 (21
(1959) 141. 1’, Hendenqrisl. M. Olwon. P. WaIlen. A. Kassman. S. Hogmark
111101
44(1990) 721.
(4 D. S. Rlckerh5, S. J. Bull. I. Roherlson and A. Hcndr~ Surf. (0,0. -
/c’I1III0L,
4/0996163.
.
- -
Ia ‘s I. C hen and J. Ci. Duh. Surf. (cult. lee/mo!., .1,5 (1991) 163. 16 K Reichel. W Brandl, M. Mack. H. H. 1-Jrlherger md H Kleini, (~,I!Icl1I0lt’c/i,iik,
Si (2 (1991)1 426.
17 .1. K. Dennis and K. S. Sagoo. tie!. I-orish.. 59(61 (jcmne( (1991) III -