Wear and performance of coated carbide and ceramic tools

Wear, 80 (1982)

239 - 258

239

WEAR AND PERFORMANCE OF COATED CARBIDE AND CERAMIC TOOLS A. K. CHATTOPADHYAY

and A. B. CHATTOPADHYAY

Department of Mechanical Engineering, West Bengal (India) (Received

May 1,1981;

in revised form

Indian Institute of Technology, January

Kharagpur

2,

7, 1982)

Summary The essential properties of modern high production cutting tools include high wear resistance, toughness, chemical stability at high temperature and under high sliding forces and a sufficiently high flow strength. It is difficult to achieve all these properties in a single tool material and techniques have been developed for coating a thin layer of a highly wear-resistant and friction-reducing material such as Tic, TiN, Ti(C,N), AlsOa and Ti(C,N,O) onto a tough and strong substrate such as cemented carbides. The performance of such coated tools and their wear mechanisms were investigated. 1. Introduction The principal properties required of a modern cutting tool material for a high production rate and high precision machining include good wear resistance, toughness, chemical stability under high temperature and large sliding forces and a sufficiently high flow strength. It is not possible to achieve all these properties, some of which are mutually exclusive, in a single material. Techniques have been developed to exploit the beneficial properties of a number of materials in a single application. One effective technique is the coating of thin layers of one or more highly wear resistant materials such as Tic, TIN, Ti(N,C), Al,Os and Ti(N,C,O) on tough and strong substrates such as conventional cemented carbides. Several coated carbide tools have been introduced and others are being developed. The characteristics, properties and fields of application of such tools vary widely. To exploit their full benefits and to develop further new coated tools, extensive study and research are necessary. Carbide tools coated with TiC were the first type introduced about 15 years ago and are still widely and advantageously used. Although superior to similar uncoated tools, the performance is restricted by a decarburized zone, the 77phase, which develops at the interface between the substrate and the coat. The 7 phase is brittle and porous so that the coating does not adhere strongly to the substrate and the tool is weakened. Venkatesh [l] , Sproul and Richaman [ 21, Sarin and Linstrom [ 31 and others studied the nature and behaviour of the ‘17phase and attempted to 0043-1648/82/0000-0000/$02.75

@ Elsevier Sequoia/Printed

in The Netherlands

240

minimize or eliminate it either by replacing chemical vapour deposition (CVD) by sputtering or carburizing before coating TiC by CVD. ’ Schintlmeister et al. [4] investigated the effect of the geometrical parameters of TiC and TiN coatings on their transverse rupture strength (TRS). Thick coatings (above 5 - 6 pm) and the presence of the r) phase reduces the TRS. An equiaxed grain structure of the coated layer provides a greater TRS than a columnar or an amorphous structure. Schintlmeister and Pacher [ 51 observed that composite coatings of TIC and Ti(C,N) performed better than a single coating of TiC or TiN. Stjenburg et al. [ 61 found that the deposition rate of TiC by CVD increases with gas pressure and CH4 content and decreases with increase in TiC14 and HCl in the gas mixture. Carson et al. [ 71 compared the wear characteristics of oxycarbide coats with respect to TiC and TiN to investigate the role of the free energy of formation on chemical stability and wear resistivity. Sadahiro et al. [8] developed a Ti(N,C,O)-type coated tool to achieve better chemical stability and wear resistance than Tic- and TiN-coated tools. Under suitable conditions and sufficiently high speeds the tool had a longer life than Tic- and Tic-AlaOs-coated tools. Karapantev [9] carried out wear tests to compare various wear criteria for different types of coated tools and conventional uncoated carbide tools and observed that tools of the TiC + Al,Os and TiN + Ti(C,N) + TiN types were greatly superior to tools coated with Tic, TIN, Ti(N,C). The authors of the present paper collected different types of coated tools from all over the world and studied extensively their constructional features, wear mechanism and relative performances. 2. Experimental investigations and discussion 2.1. Experimental conditions The experimental conditions are given in Table 1. The tool bits procured and studied are given in Table 2. The geometry of tool wear based on the measurement and assessment of wear that were carried out is shown in Fig. 1. 2.2. Form and amount of wear After machining for about 20 min at different speeds, photographs of the worn tools taken by scanning electron microscopy (SEM); these photographs are shown in Figs. 2 - 9. TABLE

1

Work material Cutting speed V, Feed S Depth t of cut Tool geometrya Tool size and shapea Environment aInternational

Organization

C-15 steel 75 - 280 m mine1 0.25 mm rev-’ 1.0 mm 5”, -5”, 5”, 5”, 15”, 75”, 0.8 mm SNUN-120408 Dry for Standardization

specifications.

241 TABLE 2 Designation

Manufacturer and country of origina

Coating composition and thickness (pm)

Substrate composition

Coating hardness WV)

TTX. (Plo 1

Widia (I)

-

55% WC, 36% TiC + TaC, 9% CO

-

TTW

Widia (I)

-

72% WC, 20% TiC + TaC, 8% CO

-

TR

Widia (I)

TIC; 10

82% WC, 8% TiC f TaC, 10% CO

3200

TG

Widia (I)

Tic; 6 - 10

81% WC, 12% TiC + TaC, 7% CO

3200

TN

Widia (I)

TiC TiN; 10

81% WC, 12% TiC + TaC, 7% CO

3200 2450

GC 015

Sandvik (S)

Tic; 5 Al,O, ; 1

WC, TIC + TaC, CO

3200 2700

ANT 5

Duracarb (H)

TLC TiN; 10

WC, Tic-TaC,

CO

3200 2450

Tic Ti( C,N)

84% WC, 10% TIC + TaC, 6% CO

3200 -

TLC Ti(CN)

WC, TIC + TaC, CO

3200

(P20

1

GM 15

Metallwerk Plansee (A)

T 530

Toshiba Tungalloy

(Jf

WIDALOX ZR

Widia (G)

-

96% A1,03, 3.5% TIC, 0.15% SiOz

-

Oxide ceramic

CGCRI (I)

-

99% A1203, 1% MgO, Cr

-

“A, Austria; G, F.R.G.; H, The Netherlands; I, India; J, Japan; S, Sweden.

RAKE

SLIDING

SURFACE

WEAR

PRINCIPAL

\ \

AUXILARY w

A

SECTION

AA

Fig. 1. Wear pattern and principal wear criteria.

FLANK

242

(a)

(d) Fig. 2. Crater wear of different tools (cutting speed, 280 m min-’ ; time, 20 min unless otherwise indicated): (a) TR; (b) TG; (c) TTX (11 min); (d) TTW (11 min). (Magnifications: left-hand side, 27~; right-hand side, 710x.)

243

(a)

(b)

(4 Fig. 3. Crater wear of different tools (cutting speed, 280 m min-’ ; time, 20 min unless otherwise indicated): (a) TN;(b) ANT 5; (c) GM 15; (d) T 530 (12.5 min). (Magnifications: left-hand side, 25X ; right-hand side, 680X .)

(a)

(b)

(c) Fig. 4. Crater wear of different tools (cutting speed, 280 m min--l; time, 20 min unless otherwise indicated): (a) ZR;(b) GC 015; (c) CGCRI (11 min). (Magnifications: left-hand side, 27~; right-hand side, 710x.)

The magnitude of crater wear was considerably reduced with all coated tools but to a different degree compared with uncoated similar tools. When machined at high speed (280 m min-‘) for 20 min it was observed that with the TR tool the TiC coating was removed from the crater. There was evidence of mechanical wear and a trace of diffusion wear on the substrate as shown in Fig. 2. With the TG material, under the same conditions, crater wear was much less and the coating although broken still remained and resisted wear (Fig. 2). With TG tools the coat is thicker and uniformly distrib-

245

(4

(b)

Fig. 5. Crater wear of different took (cutting speed, 120 m min-’ ; time, 20 min): (a) TR; (b) TG; (c) TTX; (d) TTW. (Magnifications: left-hand side, 27~; right-hand side, 710X.)

(a)

Fig. 6. Crater wear of different tools (cutting speed, 120 m min-l ; time, 20 min): (a) TN;(b) ANT 5;(c) GM 15; (d) T 530. (Magnifications: left-hand side, 27~; right-hand side, 710x.)

247

(a)

(b)

(c) Fig. 7. Crater wear of different tools (cutting speed, 120 m min-’ ; time, 20 min): (a) ZR; (b) GC 015; (c) CGCRI. (Magnifications: left-hand side, 27~; right-hand side, 710x.)

uted over the substrate with no trace of the q phase, as shown in the fractograph of Fig. 10. Figure 3 shows that, at high speed, crater wear with TiNcoated tools is less than with Tic-coated tools. Although TN (Widia) and ANT 5 (Duracarb) are said to be of the same type and construction, TN shows greater resistance to cratering because the coating thickness of TN is greater than that of ANT 5. This is clear from the fractographs of Fig. 10. Even after 20 min the coat was not totally removed from the crater of the TN tool. TN is more resistant to grooving wear. Figure 3 shows that with high speed machining the coating is totally removed, leaving a large crater in the GM 15 tool compared with all other

(d)

(e) Fig. 8 (continued).

tools coated with TiC + TiN. With T 530 and ANT 5 tools the coating, even after breaking, existed in patches on the rake. All the tools, except TN, coated with TiC + TiN suffer grooving wear. The GC 015 tool, which has a very fine layer of AlaOs about 1 pm thick over the TiC coating, does not withstand high speed and fails particularly because of severe crater and grooving wear as shown in Fig. 4. Of all the tools tested, the carbide ceramic tool ZR performed best even at high speeds. Figure 4 shows that not only is crater wear very small but there is no sign of diffusion or grooving wear which indicates that this tool is very stable, diffusion resistant and tough. The pure ceramic tool from CGCRI performed poorly (Fig. 4); it lacks toughness and mechanical wear resistance owing to its coarse grain and poor grain bonding (Fig. 10).

249

(i)

(j)

(k) Fig. 8 (continued). Flank wear of different tools (cutting speed, 280 m mine1 ; time, 20 min unless otherwise indicated): (a) TR; (b) TG; (c) TN;(d) ANT 5; (e) GM 15; (f) T 530 (12.5 min); (g) ZR; (h) GC 015; (i) CGCRI (11 min); (j) TTX (11 min); (k) TTW (11 min). (Magnifications, 27x .)

Figures 5 - 7 indicate that at medium (120 m min-’ ) speeds u all coated tools are more wear resistant than uncoated tools. Even after 20 min of machining, the coatings were intact. The small amount of wear was due to abrasion. However, it was observed that the coating was plastically deformed and displaced from the crater area towards its outer edge in the form of a ledge. This is prominent with both TiC and TiC + TiN types, including the CC 015 tool.

(a)

(e) Fig. 9 (continued).

Figure 7 shows that the carbide ceramic tools ZR are also successful at lower speed. The CGCRI tool did not work satisfactorily at low and medium speeds because of inherent weakness against chipping and fracturing. Flank wear, in the same way as crater wear, was found to be reduced by various amounts in all types of coated tools compared with uncoated tools. With Tic-coated tools, the TG grade showed much less flank wear and has been recommended for machining where a good surface finish and high productivity are desired. The nature and magnitude of flank wear, both principal and auxiliary, are shown in Figs. 8 and 9. Of TiC and TIC + TiN tools, the latter are more crater resistant and the former are more resistant to flank

251

0)

(i)

(j)

(k) Fig. 9 (continued). Flank wear of different tools (cutting speed, 120 m mine’; time, 20 min): (a) TR; (b) TG; (c) TN; (d) ANT 5; (e) GM 15; (f) T 530; (8) ZR; (h) GC 015; (i) CGCRI; (j) TTX; (k) TTW. (Magnifications, 27x .)

wear. Of the nitridecoated tools, GM 15 and to a certain extent ANT 5 were found to be resistant to both crater and flank wear. T 530 showed little crater wear but severe flank wear. This is also true for the TN tool, particularly at high speed. At low speeds of about 120 m min ’ all coated tools successfully resisted flank wear. GM 15 and T 530 suffered a little flank wear and some edge chipping which could lead to early failure. GC 015 was found to be almost as good as GM 15 and ANT 5 at resisting flank wear but suffered from thermochemical attack (Figs. 8 and 9). As with cratering wear, with flank wear the ZR tool appeared to be the most successful over the

252

(b)

(d)

w

(e)

(i)

Fig. 10. Fractographs of coated carbide and ceramic tools: (a) TR; (b) TG; (c) ANT 5; (e) GM 15; (f) T 530; (g) GC 015; (h) ZR; (i) CGCRI. (Magnifications: (d), (e) 2200x; (c), (f), (g) 2300~ ;(h) 2400x ; (i) 860x .)

TN;(d)

(a), (b),

253

(a)

(b)

333 (9

(e)

(0

(h)

(i)

(k)

Fig. ll._pter depth profiles of different tools (cutting speed, 160 m mine1 ; feed, 0.25 mm rev ; depth of cut, 1.0 mm; time, 20 min unless otherwise indicated; environment, dry; vertical magnification set at 500x; horizontal magnification set at 20x): (a) TR; (b) TG;(c)TN;(d) ANT5;(e)GM 15;(f)T 530;(g)ZR;(h) GC 015;(i)CGCRI(12.5 min); (j) TTX (17.5 min);(k) TTW (16.2 min).

-.--+ -Q-

140

20

-

l-4 I I

0

50

WIOIA

100

I I

IS0

200 SPEED,

GM I5 GC 015

TTX

i !

250 V,,

/

/

I

xx)

350

i

CUTTING

Fig. 12. Effect

I

PLANSEE SANOVIK

4( X

m /ml”

of cutting speed on the feed force for various tools.

entire range of speeds. The other ceramic tool (the CGCRI tool} suffered excessive flank wear because of brittleness. Figure 11 shows crater depth profiles of all the tools. It is evident that the nitride coating is more crater resistant than the carbide coating. TN had exceptiona~y good crater resistance, mainly because of the thick coat which remained even after machining for 20 min. Figure 11 confirms that ZR is the most stable and wear-resistant tool. T 530 suffered diffusion wear through the substrate. The dist~bution of the horizontal component of the cutting force, shown in Fig, 12, indicates that a nitride coating offers much less friction at the chip-tool interface than Tic-coated tools, as observed by other workers. Variation in the magnitude of the horizontal force in the TiC and TiC + TiN groups is attributed to differences in surface finish and edge rounding during manufacture. The excessive force with TJN is mainly for a large edge radius. In this respect ceramic-coated tools and ceramics were between the TiC and TiC + TiN groups. With time, the variation in the force would also depend on the crater profile.

255

1600 WORK CUTTING

MATERIAL: SPEED

:

FEED 1400~

DEPTH

OF

0.25

mm/

CUT:

CUTTING

REV.

DRY

1200.

1000

:TOOL

-Q--WIDADUR ‘-Q-DURACARB -nWIDALOX -PWIDADUR -.-WIDIA -A-WIDADUR -B-PLANSEE -_(-SANDVIK

1.0 mm

:

ENVIRONMENT

LEGEND

C-15 SlEEL 75 m / min.

:

-@-WIDIA --O-

-

TR ANT 5 ZR TN TlW TG GM IS CC 015 TTx 1530

-X-CERAMIC

CUTTING

Fig. 13. Average

TIME,

T. ml”.

flank wear with time for different

tools.

1600 WORK

MATERIAL

CUTTING

SPEED FEED

1400

-

DEPTH

OF

CUT

ENVIRONMENT

:

C-15

: 180 m : 0.25 : 1.0 : DRY

mml

CGCRI

LEGEND:CUTTING

STEEL /mm.

-_(-WIDADUR --o-DURACARB -A-WIDALOX --o-WIDADUR -e-WIDIA -AWIDADUR -a-PLANSEE

REV

mm.

‘Fr

-b-SANDVIK -a-WIDIA

-o-x-

0

2

4

6 CUTTING

Fig. 14. Average

8

IO TIME,

I2

14

T,min.

flank wear with time for different

tools.

TOOL TR ANT 5 ZR TN TTW TG GM IS GC 015 TTX

CEREMIC

I6

T 530 CGCRI

I8

20

256 1600

WORK

MATERIAL’

CUTTING

SPEED

FEE3 1400

DEPTH

OF

ENVIRONMENT

CUT

C 15 STEEL

LEGEND:

: 280m,mm.

,

:OZSmmjREV.

~

: ,‘Omm. : DRY

1200

CUTTING

Fig. 15. Average

flank

TIME,

160

; Y

CLJTTlNG

of crater

TR

-a--a~-m-.-----A---+-

DURACARB ANT5 WIDALOX WIDADUR TN WIDIA TTW WIDADUR TG PLANSEE GM15 SANDVIK GC 15

-Q-

WlDlA

---x-m-

CERAMIC

T, ml”

2200

Fig. 16. Rate

TOOL

WIDADUR

wear with time for different

i? ” s

CUTTING --‘&

SPEED,

growth

Vc,m/mln

of different

tools.

tools.

TTX CGCRI

257

2.3. Magnitude of wear and its rate of growth At speeds up to about 180 m min -’ the increase in the rate of flank wear of all coated and ceramic tools is much lower than that of uncoated tools (Figs. 13 and 14). However,at high speeds near 280 m min-’ the T 530 tool had a greater flank wear rate than uncoated tools (Fig. 15) because the substrate lacked diffusion resistance. CGCRI is very poor, particularly at low speeds. Figure 6 shows the growth of crater wear for various tools and verifies the observations by SEM and other studies. The magnitude of the notch width at the auxiliary flank, which influences the surface finish, is shown in Fig. 17. Tools such as ANT 5, T 530, GM 15 and ZR are expected to provide a much better surface finish.

ItSO-

WORK CUTTING

MATERIAL: SPEED:

1400-DEPTH OF ENVIRONMENT

FEED: CUT

C-15 STEEL 280m/mm.

LEGEND:CUTTING -0-WIDADUR

0.25mm/Rw. : I.0 mm.

:

-O--

DRY,

DURACAm

-A

-WIDALOX

-cl

-WlDADUR

-*-WIDIA

.-*

1200

TOOL TR ANT

-WIDADUR

TG

--r--PLANSEE 4 -SANDVIK

0

2

4

6

8 CUTTING

IO TIME,

12 T,min.

14

16

5

TN TTW GM15 GC015

18

20

Fig. 17. Growth of the notch at the auxiliary flank with time.

3. Conclusions On the basis of the test results the following conclusions may be drawn. (i) Suitable coatings could control wear and considerably improve the life of carbide tools, especially at high speed and high production rates. (ii) The problem of the q phase has been minimized if not eliminated in modern coated tools.

258

(iii) A secondary coating of TIN over the TiC coating improved crater resistance but at the expense of more flank wear when compared with a single coating of Tic. (iv) Thicker, uniform and equiaxed TiC coatings provide improved wear resistance. (v) An excessively thick coating of TiC + TiN shows greater cratering resistance but reduced resistance to flank wear. This indicates that TiN is more antidiffusive and friction reducing but less resistant to chipping, i.e. less tough, than Tic. (vi) The mechanical properties of coated tools depend not only on the composition and thickness of the coating material but also on the manufacturing technique. Thus coated tools from different manufact~ers behave differently. (vii) An alumina coating over a TiC coating enhances wear and crater resistance appreciably. (viii) Ceramic tools such as ZR, if properly manufactured with suitable additives, may be as good as the most effective coated tools and even better, especially for high production turning. A carbide ceramic tool, unlike ordinary and plain ceramic tools, was found to be very tough and could machine very efficiently at very high speeds as well as at low speeds even in lathes of medium rigidity. (ix) Plain ceramic tools such as CGCRI have potential but are not yet satisfactory, mainly because of the lack of toughness and strength of the large grains, the initial microcracking and the poor bonding. The geometry and finish also require improvement.

References 1 V. C. Venkatesh, A. S. Raju and K. Srinivasan, On some aspects of wear mechanism in coated carbide tools, Ann. CIRP, (1977). 2 D. Sproul and M. H. Richaman, Effect of the ?l layer on TiCcoated cemented carbide tool life, J. Vat. Sci. TechnoZ., 12 (4) (1975) 842 - 844. 3 V. K. Sarin and J. N. Linstrom, The effect of 17 phase on the properties of CVD TiCcoated cemented carbide cutting tools, J. ~Zeetroe~em. Soe., 126 (7) (1979) 1281 - 1287. 4 W. Schintlmeister, 0. Pacher and T. Raine, Structure and strength effects in CVD TIC and TiN coatings, Proc. 5th int. Conf. on Chemical Vapor Deposition, Electrochemical Society, Princeton, NJ, 1975, 523 - 539. 5 W. Schintlmeister and 0. Pacher, Preparation and properties of hard metal layers for metal machining and jewelry, J. Vat. Sci. Technol., 12 (4) (1975) 743 - 748. 6 K. G. Stjernber, H. Gass and H. E. Hintermann, The rate of chemical vapor deposition of Tic, Proc. Int. Conf. on Metallurgical Coatings, CA, 1976, in Thin Solid Films, 40 (1977) 81 - 88. 7 W. W. Carson, C. L. Leung and N. P. Suh, Metal oxycarbide as cutting tools materials, ASME Paper 75-WA/Prod-3, April 1975, pp. 279 - 286. 8 T. Sadahiro, S. Yamaya, K. Shibuki and N. Ujie, Wear-resistant coating of cemented. carbides and high speed steels by chemical vapour deposition, Wear, 48 (1978) 291 - 299. 9 P. Karapantev, Investigation of some wear parameters of CVD layers on carbides by SEM, Ann. CIRP, 27 (1) (1978) 79 - 85.