POWDER METALLURGY INDUSTRY, ECONOMICS, AND ORGANIZATION OF PRODUCTION

DEGREE OF CHARGING OF SURFACES POLISHED

WITH TITANIUM CARBIDE AND SYNTHETIC DIAMOND

MICROPOWDEHS

V. N. Paderno, A. N. Martynenko, and L. A. Gaevskaya

UDC 621.762 + 543 + 669.018.4

During the polishing of par ts their surfaces become charged with abrasive grains, which can markedly change many of their proper t ies , including wear res is tance , ref lect ing power, and magnetic permeabil i ty. An investigation into the relat ionship between the degree of charging and the operating proper t ies of surfaces polished with diamond pastes [1] has shown that, depending on the actual application of a polished component, surface charging may have either a beneficial or a deleterious effect upon its wear res is tance . Apart from this, the degree of charging of a rubbing surface affects the wear res i s tance of the whole frict ional pair: Abrasive par t ic les embedded in the polished par t increase the wear of the mating component.

In view of this, investigations of the finish of machined par ts should include an assessment of the degree of charging of surfaces subjected to abrasive machining. Certain aspects of the charging of surfaces during polishing with micropowders of such orthodox abrasives as e lec t rocorundum and synthetic diamonds have al- ready been investigated [1-3]. Today, however, increasing use is made of abrasive pastes based in mic ro - powders of r e f r a c t o r y compounds, for example, t ransi t ion metal carbides [4], yet up to now the charging of sur faces with these micropowders has not been investigated at all.

In the work described below a study was made of the degree of charging of commerc ia l ly pure titanium and iron with micropowders of titanium carbide produced by the reduction process and, to obtain a basis for comparison, of ASM synthetic diamonds. Abrasive finish machining was performed, by the method described in [5], in an A83-4 apparatus. The par t ic le size analyses of the synthetic diamond and titanium carbide mi- c ropowders co r re sponded to the No. 10/7 fraction. In the apparatus a p re s su re of 0.8 kgf/cm 2 was applied to the specimen, and liquid petrolatum was used as a binder.

In the f i rs t place, the possibil i ty was examined of employing existing techniques [2] for assess ing the degree of charging of surfaces polished with carbide micropowders . Because of the optical isotropy and opaqueness of carbide par t ic les , in polarized light examinations of charged surfaces , such as are normally used in studies of diamond par t ic les , it proved impossible to distinguish carbide par t ic les from surface mi- c ro i r r egu la r i t i e s causedbymachin ing . It was therefore decided to study surfaces polished with the titanium carbide micropowder by electron microscopy .

Electron mic roscop ica l examinations of charged surfaces were made by the technique described in [3], using a Ut~MV-100K electron microscope . This method made it possible to determine the number of embedded par t ic les as well as their shape, size, and charac te r of distribution on the specimen surface. The total im- puri ty contents of the commerc ia l ly pure t i tanium and iron specimens investigated did not exceed 0.01%. A study of repl icas in the electron microscope and of e lectron micrographs revealed that the embedded part icles were located in the hollows and at the edges of individual sc ra tches (Figs. 1 and 2). The maximum size of the embedded titanium carbide and synthetic diamond part ic les was 0.5 t~. In the course of polishing only single par t ic les or f ragments of completely disintegrated par t ic les became embedded in the surfaces of the metal l ic specimens. F rom Figs. 1 and 2 it can be seen that the titanium specimen surfaces were charged more intensely with synthetic diamond than with reduced titanium carbide par t ic les . Intense charging of t i ta- nium surfaces with the diamond mieropowder was revealed also by observat ions of machined surfaces in polar ized light. Being t ransparent , the embedded diamond part ic les glistened on a dark metal surface back-

Institute of Materials Science, Academy of Sciences of the Ukrainian SSI% Translated from Poroshko- vaya Metallurgiya, No. 8(176), pp. 89-91, August, 1977. Original art icle submitted September 26, 1976.

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Fig . 1. T i t a n i u m s u r f a c e p o l i s h e d with r e d u c e d t i t a n i u m c a r b i d e m i e r o p o w d e r , • 10,000.

F ig . 2. T i t a n i u m s u r f a c e p o l i s h e d with ASM s y n t h e t i c d i amond m i - c r o p o w d e r , • 10,000.

T A B L E 1. D e g r e e of C h a r g i n g of M e t a l s wi th A b r a s i v e M i e r o p o w d e r s

�9 No. ofgrains] Standard Coeff. of Metal ] Abrasive per variation polished I 1 mm 2 ! error o

Ti

Fe

ASM 57,25 =k25,41 0,444 Reduced

TiC 36,37 ~ 12,87 0,354 ASM 42,29 • 0,339 Reduced

T iC 30,22 • 9,80 0,326

F ig . 3. T i t a n i u m surface p o l i s h e d with s y n t h e t i c d i a - mond m i e r o p o w d e r , p h o t o - g r a p h e d in p o l a r i z e d l ight , • 1350.

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ground (Fig. 3). Data yielded by an evaluation of the degree of charging of the su r faces by the method of ma thema t i ca l s t a t i s t i c s a re given in Table 1. In the machining of both the t i tanium and iron spec imens the degree of sur face charging was less with the reduced t i tanium carbide than with the synthetic diamond m i c r o - powder. The values of coefficient of var ia t ion, which c h a r a c t e r i z e s the uni formi ty of dis t r ibut ion of the e m - bedded pa r t i c l e s on the spec imen surfaces~ show that the embedded t i tanium par t i c l e s were more evenly d is - t r i buted.

Inves t igat ions of the geomet r i c p a r a m e t e r s of synthetic diamond [6] and t i tanium carbide [7] m i c r o - powder pa r t i c les have demons t r a t ed that diamond pa r t i c l e s have s h a r p e r co rne r s and sma l l e r co rne r radii , as a r e su l t of which they m o r e read i ly pene t ra te su r faces being machined and become more f i rmly embedded in them. This probably means that not all diamond par t i c les a re ext rac ted onto a rep l ica . It is the re fo re r easonab le to a s sume that in our study the actual degree of sur face charging with the synthetic diamond mi - c r o p o w d e r w a s h i g h e r than that indicated by the f igures obtained.

Thus, a synthetic diamond mic ropowder charges a meta l l i c sur face m o r e intensely than does a reduced t i tanium carbide mic ropewder . In view of this , reduced t i tanium carbide mic ropowder s can be r ecommended for the finish machining of s t r e s s e d pa r t s opera t ing in rubbing units.

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LITERATURE CITED

S. T. Bura, "An invest igat ion of charged su r faces polished with diamond pas t e s , " Author ' s Abs t rac t of Candidate ' s Disser ta t ion , Bryansk (1976). Z. I. K r e m e n ' and E. A. Nepomnyashchi i , "Some fea tures of the charging of laps during polishing with ab ras ive m i c r o p o w d e r s , " Abraz ivy , No. 5, 17-20 (1964). V. N. Gridnev, "E lec t ron m i c r o s c o p i c a l invest igat ions of su r faces polished with diamond pas tes , " in: Introduction of Diamonds into Indus t ry [in Russian], Izd. NIIMASh, Moscow (1967), pp. 106-112. New Diamond Abras ive Pas tes : An Informat ion Le t te r [in Russian], Naukova Dumka, Kiev (1975). A. I. Pavlyuchuk and S. P. Sokolev, New Abras ive Pas tes for Finish Machining Operat ions [in Russian], GOSINTI, Moscow (1964). V. N. Kutyakov, "An investigation of the sur face polishing p r o c e s s , " Author ' s Abs t rac t of Candidate 's Disser ta t ion , Odessa (1971). G. V. Samsonov, L. A. Gaevskaya , and A. A. Adamovski i , "Geome t r i c p a r a m e t e r s of grains of some r e f r a c t o r y carbide m i c r o p o w d e r s , ' Poroshk. Metall . , No. 12, 83-88 (1975).

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