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W-EAR Wear 203-204 11997) 692-696

Communication

Wear behavior of Cr ion implanted pure iron under oil lubricated conditions

Dehua Yang ‘, Jianren Zhou ‘, Qunji Xue b

Currently. research on the wear map has been gaining more and more attention from IribologisIs and has led to Abe creation of a new research area of wear. In thts paper. the wear behaviors (wez mechanisms, surface morphology characteristics and wear rates) of Cr ion unplanted pore imn lubricated with liquid paaffin in a large range of sliding speed and load were sludiid. On this basis, a wear map of Cr ton rmplanted pure iron was created The wear map is divided into three regions. Tbe first is the region where ~he wear rates are in the magnitude of lo-” mm’ m- ‘_ The worn surfaces of the specimens are smoeth and covered by oxide films, and Ihe wear mechanism is mainly oxidative wear. The sscond is the micro-plowing and delamination wear region in which wear rates are about IO-’ mm-’ m-l. and the worn surfaces show shallow and wide grooves, and a spalling trace of Ratlet debris. lbe third one is the micro-cuaing dominakd region where the weax rates are more than 10.’ mm3 me ‘, and the worn surfaces have fine and deep grooves with an uneven border. 0 1997 Elsevia Science S.A. All nghts reserved.

In the basic research areas of wear, research workers attempted IO isolate and understand a single mechanism and created conditions under which this mechanism dominated [ I 1. Few people tended to focus on the relationship between various mechanisms [ 21. However, several mechanisms usu- ally operate simultaneously and interact with each other in a real tribological system. Thus. the study of the “wear mech- anisms map” has gained its soil IO develop. The concept of a wear map was first suggested by Johnson and then by Tabor m 1983. A wear map stmunarixes data and models tor wear, showing how the mechanisms interface and allowing the dominant mechanisms for any given set of wear conditions to be identified. Thus, research on the wear map has gained more and more attention from tribologists in recent years, and has led IO the creation of a new research area of wear. Several wear maps have been proposed in the last ten years

[ 3 1. Fw example, Lim and Ashby ]2] constructed the first wear map of steel under the dry friction conditions. Vingsbo and Soderberg [ 41 studied the fretting wear maps of metals and steel u r the unlubricated conditions. In addition, pea- ple have sttadii axtd proposed some wear maps of aluminum alloy ]5 1, ceramics (6-81 and cutting tools made of TiN- coated or uncoated high speed steel [ 9,101. But, so far, no

research work on the wear map of surface-modified metals has been reported.

Ion implantntion is a new technology of surface modifi- cation. The physical, chemical and mechanical properties of the ion-implanted surface are significantly different from those of the bulk. In order IO increase the tmderstnttding of wear behaviors, wear mechanisms and effects of the ion- implanted surface layer on wear, we carried out the Cr ion implantation experiments on iron, studied the wear behaviors of the ion implanted surface under the conditions of lubricated sliding, load in the range of 0.5-8 N and speed in the range of 0.75-150 mm s- ‘. On the basis of calculating wear rates and analyzing the wear mechanisms in different loads and speeds, a wear map of a Cr ion implanted iron surface was thus proposed.

2. Experiment

2. I Ion implantation

Specimens of size &?2 mm X 7.9 mm were made of pure iron and implanted by Cr ions at adose of 3 X IO” ions cm -*. The ion implantation of specimens were performed using a metal vapor vacuum arc (MEWA) ion source implanter.

cGt3-lb38/97/Sl7 M) 9 1997 tshed by Etsevrrr Scxnce S A. All n&ts reserved PNSOO43-1648(96)07382-6

D. Vu&? era!. /Wear 203-204 (1997) 692496 693

Table I The p-ten of Cr ion implantstlon info pure iron

Cr’.Cr”.Cr”’ 1.99 36kV S 150°C 3mA 3xlO”mnrcm~

The detailed description of the ion implanter can be found in

Ref. [ I I]. The ion implantation parameters are summarized

in Table 1.

2.2. X-ray photoelectron spectroscopy

After ion implantation, the specimen surfaces were ana-

lyzed by X-ray photoelectron spectroscopy (KBS) on a VG ESCA LAB-210 Electron Spectrometer using the Mg Ku

line. The pass energy was 50 eV and the binding energy of C Is (284.6 eV) was used as a reference in XPS analysis. To

get a thorough knowledge of the distribution of the elements

2.3. Friction and wear tests

The friction and wear tests were carried out on a SRV

fretting wear machine and a dynamical friction coefficient measurement apparatus (DIM). The contact between the

friction pair was ball on Rat. The GCrlS bearing steel spheres with the compositions shown in Table 2 and a hardness of

HRC62 have reciprocating motion on dre surface of tbe flat

specimens. Liquid paraffin with a boiling point of 300 “C, a

density of 0.86 g cme3, viscosities of 10.28 mm2 s- ’ and

3.36 mm* s- ’ at 50°C and 100°C respectively, and with no additives, was selected as a lubricant. The wear test parame- ters on DFM are 4.5 mm in stroke, OS-3 N in load, 0.7%

2.58 mm s - ’ in speed, and 500 cycles in reciprocating num- ber. The wear test parameters on the SRV wear machine are

I.5 mm in amplitude, 2-8 N in load, 30-150mms- ’ inspeed

and 20 min in time. After wear tests, the wear scar profiles were measured using a protilometer. Since dte area of the

cross-section profile multiplied by the distance of single pass indicates the wear volume, the wear rate can thus be obtained

Table 2 Chemical compositmns of the GCrlS beanng sted sphere

C CI SI Mtl S

095-1.05 I3C-165 0.15-035 0.2&0.40 0027 COO2 balance

by further calculation. All the average values of three tests.

wear data given are

3.2. Wear scar morphology examination and wear mode

identtjbtion

The detailed examination of wear scars after friction and wear tests at various sliding speeds and loads were performed

6% D Yang c, al / Weur 2M204 (1997) 6926%

~=,g I XPS depth profiler of 3x IO” mm cm ’ Cr ion m9hntcd pure eon. (a) C Is. (b) 0 Is. (c)Fe 2p. cd) Cr 2p

on an EPMA-8 IO Elecrron Probe Mvzro-analyzer. The exam- Macon and analqsla resuks shows that worn specimen SW-

faces habc three typlcal ktnds of morphologles (see Fig. 2). Some uear scar surfaces hake a relatively flat and smooth top x uh a hghl-brw n color film of oxldes. probably a mixture

of the iron oxides. The fine and dense oxide films on the worn

surfaces can be easily seen by bolh optical and SEM obser- vatlon as shown in Fig. 21 a). These are the typlcal charac- tenstlcs of oxidation wear [ 121. Some wear scars have bright metalhc appearance with little covered by the oxide film.

D. i’an~ era/. / War 203-204 (199) 6926% 695

Rg 2 SEM mxrognphs of the sltdmg wear tracks on the surface of Cr ion implanted pure imn: (a) load. 2 N: speed. 150 mm SC’. (b) load. 2 N. speed. 60 mm s- ‘: (cl load. 2 N; speed. 0 75 mm s-’

There are fine, dense and deep grooves on their surfaces. The grooves are parallel to the sliding direction while some of 10

them have an uneven border. The grooves were formed by micro-cutting of wear counterpart asperities and wear debns

(see Fig. 2(b) ) [ 13-151. The rest of the wear scar surfaces have shallow and wide grooves with even borders, and also

some traces of spa!@ flatlet wear debris. A small amount z ::

of oxide film was observed on this kind of worn surfaces (see ,o 1 Fig. 2~). These features are the characteristics of the micro- plowing and delamination wear [ 13,141. which indicates

micro-plowing and delamination wear are the dommated wear mechanisms in the wear processes.

Wear map constmct~on

The wear rates of the specimens at each one of the wear Cg 3 War map of the IOR implanted pure KOII lubnwted wth bqutd conditions were calculated, and then the wear rates and the paraffin

6% D Yang e, ul / Wear 203-204 f 1997) 692696

related wear mechanisms were correlated IO each other. It can

be found that oxidative wear is corresponding to the lowest wear rate (about IO-6 mm’ m-l). The wear rate of micro-

plowing with delamination wear mode is about IO-’ mm3 m _ ‘. The micro-cutting wear mode has the hugest wear rate (more than 1O-J mm3 m-‘). Thus by selecting slidingspeed and load as axes and plotting wear mechanisms and wear rate data on the logarithmic coordinate scale, the wear mechanism

map (as shown in Fig. 3) of Cr ion implanted pure iron under

lubrication can be obtained. From the analysis of wear data,

it is known that the wear rates and related wear modes change

continuously from one area of the wear map to another, with-

out any abruption. One of wear mechanisms dominates in a particular area, but the others may also exist with small

effects.

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of Mu~erids. Apnl P-13. 1989. Dmvrr. CO, T&American Seciety r,l Mechanical Engmeers. New York, pp. 723-728.

I71 S.M. Hsu. D.S. Lim, Y.S. Wang and R.G. Munm. Lubr. Eng.. 57 (1991)49-54.

181 A Skopp. ht. Woyat and K.H. Habig. Wear. /RI-Ii?3 (1995) 571- 580.

l9l SC LimY 6.Lw.S H.LeeandK.H.W Sah, Wear. 162-164( 1993) 971-974.

1101 S.C.Lim,C.Y.H.LimandK.S.Lee.Wcur, IRI-183(1995)901-912. [Ill W.L. Lin.XJ.DinS.H.X.ZhanS.J.M. SanS. 1. Xuan6Z.Y. Wang,

SIlljI cwr. rcchnol.. 51 ( 1992) X34-539. [ 121 L. Rapopon. Wear. 181-183 (1995) 28%289. I131 C.-G. Li. Q.-D. Zhw. G.-S. Song and ZS. Fang. Wear. 162-161

(1993) 75-82. II41 B. Zhang. Y. LIU and W. Shen. Wear. 162-l&1 (1993) 61 t-613. I I51 A Ravtkiranand B.N RamilaBai. Weur. /RI-I83 ( 1995) -550.

Biographies

Xefemkces Jianren Zhou is an Assistant Professor in Department of

Mechanical Engineering, Prairie View A&M University, Texas, USA. He received his Ph.D. in Mechanical Engineer-

ing from Iowa State University in 199 I. He is currently work- ing on several research projects funded by government agencies, national laboratories, and industries. These research

projects include areas of tribology, thin films. chemical vapor

deposition, emission control, polymeric composites, and manufacturing processes.