Abstract
An article of manufacture and method of forming a borided material. An electrochemical cell is used to process a substrate to deposit a plurality of borided layers on the substrate. The plurality of layers are co-deposited such that a refractory metal boride layer is disposed on a substrate and a rare earth metal boride conforming layer is disposed on the refractory metal boride layer.
Claims
1. A method of forming a boride material on a substrate, comprising the steps of, providing a boriding component; providing a substrate having a metal alloy having a first metal constituent comprising tungsten (W) and a second metal constituent comprising rhenium (Re); disposing the substrate and the boriding component in an electrochemical bath; establishing the electrochemical bath at a temperature of about 900-1050 C.; and forming a first metal constituent conforming boride layer comprising WB.sub.4 on the substrate and a second metal constituent conforming boride layer comprising ReB.sub.2 on the first metal constituent conforming boride layer.
2. The method of forming a boride material on a substrate of claim 1, wherein the metal alloy consists essentially of WRe 25% alloy.
3. A method of forming a boride material on a substrate, comprising the steps of, providing a boriding component; providing a substrate having a metal alloy having a first metal constituent comprising tungsten (W) and a second metal constituent comprising rhenium (Re), the metal alloy consisting essentially of WRe 25% alloy; disposing the substrate and the boriding component in an electrochemical bath; establishing the electrochemical bath at a temperature of about 900-1050 C.; and forming a first metal constituent conforming boride layer on the substrate and a second metal constituent conforming boride layer on the first metal constituent conforming boride layer.
4. The method of claim 3, wherein the first metal constituent conforming boride layer comprises WB.sub.4 and the second metal constituent conforming boride layer comprises ReB.sub.2.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1(a) illustrates a conventional molten electrolyte boriding system; FIG. 1(b) shows a pack boriding system (inset) and boride layer versus boriding time plot; and FIG. 1(c) shows an electrochemical boriding system (inset) and boriding layer versus boriding time plot;
(2) FIG. 2 is an optical micrograph of multiple boride layers on a tungsten (W) carbide substrate;
(3) FIG. 3 illustrates hardness values for selected spots in an optical micrograph of WCNi6% alloy at 560 g load;
(4) FIG. 4 illustrates an X-ray diffractometer scan of intensity versus 20 at a 1 glancing angle scan of a multi-layered boride for a WCCo 6% substrate;
(5) FIG. 5(a) is an SEM micrograph of separate ReB.sub.2 and underlying WB.sub.4 conformal layers on a WRe alloy substrate with selected hardness values shown; FIG. 5(b) shows a plot of load (mN) versus penetration depth in nm for load application and unloading;
(6) FIG. 6(a) is a higher magnification SEM micrograph of the alloy of FIG. 5(a) showing layer thicknesses for ReB.sub.2 and WB.sub.4 on the WRe substrate; FIG. 6(b) illustrates a plot of load (mN) versus penetration depth in nm for load application and unloading;
(7) FIG. 7 shows an X-ray diffractogram of intensity versus scattering angle 2 showing a mixture of ReB.sub.2 and WB.sub.4 layers with a top conformal layer of ReB.sub.2 determined by glancing angle 1 scan and the inner conformal layer of WB.sub.4 by a regular 2 scan;
(8) FIG. 8(a) shows a micrograph of a boriding WC surface with hardness values at selected positions and FIG. 8(b) shows hardness values in a micrograph of a borided WCNi 6% alloy at 50 g load;
(9) FIG. 9 shows X-ray diffractograms in intensity versus 2 with indicators at diffraction peaks characteristic of CoB, WB.sub.4 and WC;
(10) FIG. 10(a)-10(c) show micrographs of a borided WRe alloy which has undergone wear testing against a fully hardened AISI 52100 grade steel ball and FIG. 10(d) shows coefficient of friction over time for testing of the borided WRe alloy;
(11) FIG. 11(a) shows an SEM image of the surface of a borided WRe of FIGS. 10(a)-10(d); FIG. 11(b) shows a cross section of the tested borided WRe layer and surface; FIG. 11(c) shows a profilometer scan of the cross section of FIG. 11(b) and FIG. 11(d) shows a 3-D profilometer plot of the cross section of FIG. 11(b);
(12) FIGS. 12(a)-(c) show micrographs of a borided WRe alloy surface versus an alumina ball () at 50 rpm, at 2N load for 1 h at room temperature; and FIG. 12d shows a plot of coefficient of friction versus time for the wear test of FIGS. 12(a)-12(c); and
(13) FIG. 13(a) shows an SEM image of the surface of a borided WRe surface from the test of FIGS. 12(a)-12(d); FIG. 13(b) shows a cross section of the tested borided WRe surface; FIG. 13(c) shows a profilometer scan of the cross section of FIG. 13(B); and FIG. 13(d) shows a profilometer 3D image from the scan of FIG. 13(c).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(14) In FIGS. 1(a)-1(c) are shown various systems 10 and methods for performing boriding operations. In the preferred embodiment of the invention the system and method of FIG. 1(c) is utilized. In FIG. 2 is shows an optical micrograph of an article of manufacture having multiple boride layers 12, 14 and 16 disposed on a WC substrate 18. These layers 12, 14 and 16 are a combination of tungsten boride phases including WB.sub.4, W.sub.2B.sub.5 and WB.sub.2. Layer thicknesses can be varied by careful selection of electrolyte salt bath composition, and this process is preferably carried out at temperatures between about 900-1050 C.
(15) FIG. 3 is a micrograph of a cross section of a boriding WCNi6% alloy. Also shown are hardness values at selected locations, and the hardness values on these boriding tungsten carbide surfaces were in the range of about 31 GPa to 35 GPa. Preliminary results for the boriding of WCNi6% alloy showed excellent hardness values in the range of superhard materials. Further studies were conducted for the boriding of WCCo6% alloy and X-ray diffraction pattern (both in regular 2 and 1 glancing angle modes) of the processed alloy is given in FIG. 4. The X-ray diffraction indicates that there are two possible phase formation after applying boriding process one of which is CoB phase and the other is WB.sub.4 phase formation. Borided WCCo6% alloys are found to have hardness values in the range of 11-12 GPa.
(16) FIG. 5(a) shows superhard rhenium diboride and tungsten tetraboride phases disposed as separate layers obtained on the WRe 25% alloy having a thickness of about 19 and 10.7 m respectively. The formation of such superhard borides with very large thicknesses was achieved by a simple diffusion based conversion coating process which cannot be achieved by any deposition method (PVD or CVD). FIG. 5(a) also shows the hardness at selected locations of the superhard borides ReB.sub.2 and WB.sub.4 in the range of 36-46 GPa with 500 mN of load. FIGS. 5(b) and 6(b) show load/unload plots as the function of penetration depths of the inner WB.sub.4 and the outer ReB.sub.2 layer, respectively.
(17) Boriding can also be done on all kinds of metallic and alloy surfaces including ferrous alloys, magnesium-base alloys, titanium base alloys, aluminum-based alloys, cobalt, cobalt and chromium based alloys, nickel, tantalum, zirconium, molybdenum, tungsten, niobium, hafnium, and rhenium. These borided metal and alloys can be used in various manufacturing and transportation applications such as metal forming tools, fuel injectors, gears, bearings and some of the power- and drive-train applications in cars and tracks.
(18) Further, FIGS. 5(a) and 6(a) show confirmation of the layered structure of the ReB.sub.2 outer layer 2, underlying WB.sub.4 layer 22 and the substrate 24 of WRe alloy. The ReB.sub.2 outer layer 2 was determined by glancing angle 1 scans of 2 for an X-ray diffractometer (see FIG. 7). A regular 2 X-ray scan (see FIG. 7) was used to identify the underlying WB.sub.4 layer 22 which also had some ReB.sub.2 phase intermixed; and the substrate 24 was identified by a routine 2 X-ray scan.
(19) In yet another embodiment of the invention a borided WCNi6% alloy substrate was obtained by the method shows in FIG. 1(c). The micrograph of FIGS. 8(a) shows the hardness values at selected locations of the cross-section, and FIG. 8(b) shows the various layer thicknesses.
(20) In yet another embodiment of the invention a WCCo6% alloy substrate was borided; and the X-ray scan of FIG. 9 show an outer layer of CoB and an inner layer of CoB+WB.sub.4. The use of Co as a binder hinders formation of WB.sub.4 as compared to Ni (see FIGS. 8(a) and 8(b)). The hardness values for W-6% Co were also 11-12 GPa versus 31-35 GPa for the Ni alloy of FIGS. 8(a) and 8(b). These can be compared to hardness values of diamond 115 GPa; CBN; 48 GPa; B.sub.4C; 30 GPa; and OsB.sub.2 37 CPa.
(21) The following non-limiting Examples illustrate various aspects of the invention.
Example I
(22) Wear testing was performed for a borided WRe alloy against a diameter wear ball of 52100 steel at room temperature, and ball rotation rate of 50 rpm at a load of 1N. As shown in FIGS. 10(a)-10(c), the wear surface shows no abrasion of the wear surface; and FIG. 10(d) shows coefficient of friction versus time for a 1 h test.
(23) FIGS. 11(a)-11(d) confirm the layer depositions on the substrate and that virtually no wear occurred to the borided surface.
Example II
(24) Wear testing was performed for a borided WRe alloy against a diameter alumina ball for the same operating conditions as Example I. As shown in FIGS. 12(a)-12(c) the wear surface shows no abrasion of the borided surface and FIG. 12(d) shows coefficient of friction versus time for the 1 h test. FIGS. 13(a)-13(d) show an SEM image of the surface of the borided WRe surface after the test shown in FIGS. 12(a)-12(c). FIG. 13(b) shows a cross-section of the tested, borided WRe surface; and FIG. 13(c) shows a profilometer scan of the cross-section of FIG. 13(b). FIG. 13(d) shows a profilometer 3D scan image from the scan of FIG. 13(c).
(25) The foregoing description of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.
