US3674574A - Nitrided surface modified alloys - Google Patents

Abstract

GRADED NITRIDED ARTICLES, SURFACE MODIFIED IN ALLOY COMPOSITION WHEREIN THE SURFACE ZONE CONSISTS OF NITRIDED ALLOYS CONSISTING ESSENTIALLY OF (A) ONE OR MORE METALS OF THE GROUP COLUMBIUM, TANTALUM, AND VANADIUM; (B) TITANIUM; AND (C) ONE OR BOTH METALS OF THE GROUP MOLYBDENUM AND TUNGSTEN. A MINOR PORTION OF THE NITROGEN MAY BE REPLACED BY OXYGEN OR BORON. NITRIDED MATERIALS PREPARED FROM HOMOGENEOUS ALLOYS ARE ALSO INCLUDED. THE MATERIALS ARE CHARACTERIZED BY EXCELLENT WEAR AND ABRASION RESISTANCE.

Description

United States Patent O 3,674,574 NITRIDED SURFACE MODIFIED ALLOYS Ray J. Van Thyne, Oak Lawn, and John J. Rausch,

Antioch, Ill., assignors to Surface Technology Corporation, Stone Park, Ill.

No Drawing. Continuation-impart of application Ser. No. 755,658, Aug. 27, 1968, now Patent No. 3,549,427. This application Mar. 4, 1970, Ser. No. 16,595

Int. Cl. C22c 27/00; C23c 11/14 US. Cl. 14831.5 2 Claims ABSTRACT OF THE DISCLOSURE Graded nitrided articles, surface modified in alloy composition wherein the surface zone consists of nitrided alloys consisting essentially of (A) one or more metals of the group columbium, tantalum, and vanadium; (B) titanium; and (C) one or both metals of the group molybdenum and tungsten. A minor portion of the nitrogen may be replaced by oxygen or boron. Nitrided materials prepared from homogeneous alloys are also included. The materials are characterized by excellent Wear and abrasion resistance.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our pending application Ser. No. 755,658, entitled Wear Resistant Materials, filed Aug. 27, 1968, now U.S. Pat. 3,549,427.

BACKGROUND OF THE INVENTION In our parent application, Ser. No. 755,658, referenced above, we have disclosed and claimed certain nitrided alloys consisting essentially of (a) at least one metal of the group columbium, tantalum and vanadium;

(b) titanium; and

(c) at least one metal of the group molybdenum and tungsten in certain percentages by weight and compositional relationships as are therein set forth. Such nitrided materials are characterized by, among others, excellent wear and abrasion resistance and offer substantial utility as cutting tool materials.

In such parent application, we have noted that the desired alloys to be nitrided may be formed as free standing thin sections or clad or by various means formed as a coating upon different substrates. Similarly, in such parent application, we have noted that a variety of nitriding treatments may be employed to effectuate the desired results.

In the present application, we wish to elaborate upon the teachings of said parent application. The compositions hereof which are nitrided or otherwise treated are the same as the alloy compositions which are disclosed in our parent application.

Accordingly, our parent application, Ser. No. 755,658, now US. Pat. 3,549,427, in its entirety, is incorporated herein by reference. We would note that a counterpart of such parent application has issued as Belgium Pat. 720,- 398. As will be evident, we herein provide additional features to said basic invention and certain improvements thereof.

In our parent application, the temperatures are presented uncorrected. In the present application, temperatures are corrected. We used a correction factor determined by using a tungsten-rhenium thermocouple in conjunction with the sightings of the optical pyrometer mentioned in the parent case.

Furthermore, we would note that it is well known that titanium can be nitrided to form a hard surface layer thereon but such material shows a chipping propensity due to Patented July 4, 1972 brittleness. In the practice of our invention, such brittleness is avoided by specific alloying as taught herein prior to nitriding. Additionally, the alloying elements present in typical commercially available titanium alloys do not produce the same improvement and nitrided commercial titanium alloys show chipping similar to nitrided titanium.

The nitriting of titanium-rich alloys, i.e. containing about percent titanium has been studied previously (for example, see E. Mitchell and P. J. Brotherton, J. Institute of Metals vol. 93 (1964) p. 381). Others have in estigated the nitriding of hafnium-base alloys (F. Holtz et al., US. Air Force Report IR-718-7 (II) (1967)); molybdenum alloys (U.S. Pat. 3,161,949); and tungsten alloys (D. J. Iden and L. Himmel, Acta Met. vol. 17 (1969), P- 1483). The treatment of tantalum and certain unspecified tantalum base alloys with air or nitrogen or oxygen is disclosed in US. Pat. 2,170,844 and the nitriding of columbium is discussed in the paper by R. P. Elliott and S. Komjathy, AIME Metallurgical Society Conference, vol. 10, 1961, p. 367.

In the present application, we wish to clearly point out the significance of alloying surface treatments or coatings or claddings with the present materials and surface treatments wherein nitriding is employed as the major constituent along with relatively minor amounts of oxygen and/or boron.

It should be noted that the alloys of the present invention may be employed on another metal or alloy as a surface coating or cladding and with the proper substrate selection, a highly ductile and/or essentially unreacted substrate can be obtained. For example, columbium or tantalum are much less reactive to nitrogen when used in conjunction with the alloys hereof and tungsten and molybdenum do not form stable nitrides at the nitriding temperatures employed. Spraying and/ or fusing the desired alloy onto the surface are included in the various coating methods available. A variety of direct deposition methods may be employed or alternate layers could be deposited followed by a diffusion annealing treatment.

As set out in our parent application in determining whether or not a material falls within the scope thereof, certain test criteria were used as are set forth therein. More particularly, following nitrided sample preparation lathe turning tests were run thereon at surface speeds from to 750 surface feet per minute (SFM) on A181 4340 steel having a hardness of around Rockwell C, (Re), 43 to 45. A feed rate of 0.005 in./rev. and depth of cut of 0.050 in. were used. A standard negative rake tool holder was employed with a 5 back rake and a 15 side cutting edge angle. Tool wear Was measured after removing a given amount of material.

The principal criterion in our parent application in determining whether the nitrided materials pass or fail and thus whether or not they are included or excluded from the scope thereof was the ability to cut 2 cuubic inch metal removal of the 4340 steel at speeds of both 100 and 750 s.f.m.

At 750 s.f.m. our high performance, nitrided materials readily pass the initial test of 2 cu. in. metal removal in about 1 minute. (We would note that by s.f.m. is meant the linear rate at which the material being cut passes the cutter.)

In some aspects of the present invention, such test criteria of the parent application are inoperative. This is particularly true of the thin sections and surface zones considered herein. The nitrided alloys are the same but in some instance in thin sections the test criteria of the parent case are not met herein. However, the materials still offer substantial wear and abrasion resistant properties.

In evaluating tools and tool materials, failure is often assumed to occur when the wearland reaches 0.030 inch.

With the materials of this invention, We selected a rather severe testwe indicate those which are good (i.e., pass, the test), when a 750 s.f.m. and 2 cu. in. removal, there is a uniform wearland of less than 0.025 in. Furthermore, we would note that although chipping is seen in some compositions upon testing at 750 s.f.m. the chipping propensity is aggravated at lower speeds and better assessed at 100 s.f.m. The latter is one of the reasons for selecting both speeds.

Accordingly, a principal object of our invention is to proivde certain novel articles wherein the surface zone thereof is a nitrided alloy consisting essentially of: (a) at least one metal of the group columbium, tantalum and vanadium; (b) titanium; and (c) at least one metal of the group molybdenum and tungsten.

Another object of our invention is to provide said novel articles aforesaid wherein up to three percent of the titanum content is replaced by zirconium.

A further object of our invention is to provide such nitrided articles wherein the nitrogen pickup is at least 0.1 milligram per square centimeter of surface area.

Still a further object of our invention is to provide such nitrided articles wherein up to twenty-five percent of the nitrogen Weight pickup is replaced by oxygen and/or boron.

These and other objects, features and advantages of our invention will become apparent to those skilled in this art from the following detailed disclosure thereof.

DESCRIPTION OF THE INVENTION An alloy of the composition Cb-20V-40Ti-10Mo was readily reduced to foil by rolling and coatings thereof were made on molybdenum by fusing this alloy in argon at a temperature of about 3375 F. for a time of two minutes. The coating wet the substrate well, did not flow excessively, and did not seriously react with the molybdenum. A specimen with a 22 mil coating was nitrided at 2950" F. for two hours and showed a microhardness grading and structure similar to the nitrided material in bulk form. The microhardness at a depth of /2, 1, and 2 mils was 2190, 1600, and 1365 DPN, respectively. A coating of similar thickness was produced on tungsten by dipping tungsten stock into molten Cb-18Ti-l8W alloy.

A 3 mil coating of Cb-2OV-40Ti-l0Mo was also produced on molybdenum by fusing in argon. This was subsequently nitrided at 2250 F. for one-half hour resulting in a nitrogen weight pickup of 1.6 mg. per sq. cm. The microhardness at a depth of mil from the surface was 1680 DPN. The nitriding temperature is sufficiently low that such alloys may be coated on a variety of substrate materials including ferrous alloys and successfully nitrided to produce a hard surface.

Much thinner coatings are readily produced by similar or other procedures. As the reactive alloy coating becomes thinner, the amount of nitrogen pickup for surface hardening is reduced since the nitriding is concentrated near the surface. Accordingly, in such thin sections the depth of hardening is reduced. In relatively thin coatings, the Weight pickup of nitrogen may be 0.1 to 1 mg. per sq. cm. or less and in thicker coatings the pickup will be over 1 mg. per sq. cm. of surface area.

In our copending, referenced parent application, we have shown that for noncoated homogeneous alloy stock the amount of nitriding required for equivalent surface hardening is dependent upon sample thickness. As the thickness is decreased, the required nitriding temperature and weight pickup are reduced. We have observed a pronounced effect of specimen thickness, particularly at knife edges where the required nitrogen pickup is greatly reduced. Also, such coated or homogeneous materials may be used for a wide variety of applications requiring wear and abrasion resistance where the requirement for surface hardness or depth of hardening may be less than that required for metal cutting. Accordingly, in thin sections of homogeneous alloy material, similar to thin coatings of the alloys, the weight pickup of nitrogen may be 0.1 to 1 mg. per sq. cm.

Another useful method for utilizing our nitrided materials involves controlled evaporation of titanium from the surface of an alloy (detitanizing). By this procedure, an alloy, for example, with a titanium content greater than that determined by our compositional limitations, can be depleted in titanium content to bring the surface alloy content within our prescribed ranges prior to nitriding. We have heated various alloys containing the required metals of our invention in vacuo at temperatures below the melting point of the alloy. Titanium evaporation occurred without any substantial change in geometry. Most importantly, this was accomplished without the occurrence of significant amounts of porosity. Electron microprobe analyses confirmed the significant changes in weight that had been observed. A specimen of Cb-45Ti-1OM0 vacuum treated at a pressure of 5X10 torr at 2850 F. for four hours showed a decrease in titanium content and a corresponding increase in columbium and molybdenum content. The decrease in titanium content extended to a considerable depth and in the outer 2 mils the decrease was about 10 percent. Other vacuum treatments run at 2950 F. for six hours showed even greater titanium loss. A Cb-45Ti-20W alloy vacuum treated at 2850 F. for four hours lost 33 mg. for a x x A; inch specimen weighing 1.9 gram, and a similar size sample of Cb-SOTi-ZOW vacuum treated at 2950 F. for 6 hours lost 60 mg.

Similar detitanizing effects were shown for Ta-Ti-Mo alloys wherein substantial weight losses of titanium were observed without geometry changes or the development of significant amounts of porosity. Ta-40Ti-10Mo, initially 2.4 g., vacuum treated at 2950 F. for 6 hours lost 54 mg. for a X /8 x A; sample. Upon nitriding at 3250 F. for 2 hours, this material cut at both 750 and s.f.m. All such vacuum treated materials show high surface hardness. It will, of course, be appreciated that such surface evaporation techniques can be applied to alloys that are already within our prescribed composition ranges to effect desirable structural and property changes.

The cutting performane of such Cb-40Ti-l0'Mo vacuum treated at 2850 F. for 4 hours prior to nitriding at 3250 F. was better than the same alloy when nitrided without prior detitanizing. It should be noted that annealing per se, that is, annealing under conditions where significant evaporation does not occur, has an effect on the microstructural morphology. Such morphology effects due to annealing, which result in greater regularity of structure may produce improvements for certain uses, but the compositional eifect due to treatment in vacuo is of value by itself.

Since our nitrided materials present as a homogeneous material or as a coated article are in a thermodynamically metastable condition, those skilled in the art will realize that a variety of heat treatments, including multiple and sequential treatments, can be used to modify the reaction structure and resulting properties whether performed as part the over-all nitriding reaction or as separate treatments. Improvement in cutting properties has been noted by nitriding at lower temperatures for longer hues and by nitriding at lower temperatures followed by nitriding at higher temperatures. However, the required weight pickup for cutting at 750 s.f.m. is similar to the amount of nitriding necessary with a simple 2-hour nitriding treatment. The treatments have included typical nitriding followed by aging at lower temperatures in argon or nitrogen. We have also nitrided at higher temperatures (and longer times) that normally would produce some embrittlement and then subsequently annealed in inert gas or at various partial pressures of nitrogen as a tempering or drawing operation to improve toughness. This duplex treatment results in a greater reaction depth with the hardnesstoughness relationship controlled by the tempering temperature and time.

Such treatments can be employed to modify the properties of our nitrided materials to produce various combinations of hardness and toughness. The required annealing treatment is dependent upon the material usage, alloy composition and degree of prior nitriding.

The influence of annealing under various conditions for a variety of nitrided materials may be seen from the data presented in Table I.

6 Cb-30Ti-10Mo was reacted in an atmosphere starting with 0.45% N balance argon and ending with 0.03% N A specimen treated in this manner cut well at both 750 and 100 s.f.m. The alloy Cb-SOTi-lOMo falling outside our invention, was nitrided in A-0.1% N for 2 hours at 3050 F. Similar to treating in nitrogen, the result was a thick continuous 3 mil TABLE I Nitrldlng Argon Mlcrohardness (DPN) at treatment treatment depth (mils) Alloy composition F. Hrs. F. Hrs. 0.5 1 2 4 8 Cb-17T1-20W 3,450 2 None 2,570 2,000 1,890 1,140 000 Cb-17Tl-20W 3,450 2 3,450 1 1,220 1,017 1,040 857 Cb-l7'1l-20W 3,450 2 3,450 1 1 2,100 1,420 1,250 830 705 Cb-17Ti-20W 3,450 2 3,250 2 3, 000 2,000 ,570 2,100 925 Ta-20Ti-10Mo 3, 550 2 None 2,00 1,075 1,480 1,110 Ta-ZOTl-IOMo 3, 550 2 3,250 1 1,090 1,175 1,250 940 Ta-ZOTi-IOMQ 3, 550 2 3,250 4 1,790 1,100 900 1,000

1 Argon, 0.1 percent nitrogen atmosphere.

The alloy Cb-17Ti-20W, nitrided at 3450 F. for 2 nitride surface layer and such material fails immediately hours shows substantial softening when subsequently 2111- in testing at 750 s.f.m. These various alternate nitriding nealed in argon for 2 hours at this same temperature. If treatments may be applied to the materials of our inventhe annealing is carried out in an atmosphere of tion whether used as a homogeneous alloy or as a coated A-0.l% N it may be noted that only a moderate decrease or surface modified material. In all of the nitriding treatin hardness occurs and the material grades uniformly in ments and particularly for those involving reduced nitroa manner similar to the nitrided condition. If annealed gen potential, the effect of the varying stabilities of the at 3250 F. for 2 hours in argon the material hardens metal nitrides must be considered since this can also consignificantly. The influence of annealing in argon on tribute to surface compositional effects. reducing the uniform hardness gradient for the nitrided Surface alloying techniques are also useful for the Ta-20Ti-l0Mo alloy may also be seen from the above preparation of the alloys to be nitrided to produce the madata. We have found that nitrided alloys containing higher terials of our invention. Cb-10Mo was titanized at 2950 amounts of tungsten or molybdenum soften readily when F. for 3 hours in vacuo by holding in a pack of fine titanannealed in argon. To control this s g, that is, ium sponge which causes diffusion of titanium into the avoiding the formation of a surface-layer that is too surface. This treatment resulted in a 6 mil titanized layer soft to cut the hardened steel at 750 s.f.rn., we have found which upon nitriding for 2 hours at 3250 F. yielded a regulation of the nitrogen content of the atmosphere to graded reaction zone similar to Cb-Ti-Mo materials. This be a useful parameter. It should be noted that the contrasts with the 4 mil continuous nitride layer formed A-0.1% 2 atmosphere Will harden unnitfided of on Cb-lOMo without the prior titanizing treatment which erately nitrided alloys but results in softening when used hibit ki of h continuous i id layen With the highly nitrided alloys in the examples above- In the present invention, as in the invention disclosed A x /8 x Vs inch specimen of Cb-3OTi-20W reacted in and claimed in our copending parent application, when nitrogen at 3250 for 2 hours, Cuts Well at 750 one wishes to determine whether or not the material is use- W q ly treated P f 2 for 2 hours ful in the nitrided state for purposes hereof certain comthis material contrnues to n1tr1de as ev1denced by a further i i l ratios and f ul must be employed in some 8 mg. pick-up. cases. Such formulae represent linear proportionate A number of our materials have been n1tr1ded and subamounts based on weight percentages q y annealed- Although the flltflded alloy A modest mathematical statement is required. In the Cb 20v 40Ti 10Mo rfiresent disclosure and claims, the following ratios shall ave the followmg meanings:

passed our cutting test criteria at 750 and 100 s.f.m., im-

provement was achieved by nitriding at 3250 F. for 2 ob hours followed by annealing in argon at 3250 F. for one Ratio A= hour. Also, good combined performance at 750 and 100 a+v s.f.m. was shown for Cb-30Ti-20W nitrided at 3550 F.

for 2 hours and annealed at 35505 F. for 1 houn Almeal (That IS, the concentration of columbium to total columing at 3250 F. for one hour did not produce any signifitantalum and Vanadium) Similarly,

cant improvement and annealing for 4 hours at 3550 F.

resulted in failure in cutting at 75 0 s.f.m. Thus, one should T use due care in annealing conditions. Rat) B: my;

In most of our materials, the hardness (and nitride content) grades and lessens as one moves from the sur Ratio V face inwardly. However, We would note that in some cases Ob+ Ta V such grading extends from a plateau or from a peak hardness slightly below the surface and grades inwardly Ratio MO therefrom. Such materials can be effective cutting tools dor abrasion resistant articles.

We have also nitrided materials directly in an environ- Ratio E= ment sufiiciently low in nitrogen potential that the effect is M0 W noted. Nitriding in flowing A-0.1% N produces reduced nitrogen pick-up compared to 100% nitrogen. Another When, in the present alloy systems, more than 1 metal method involves sealing the furnace with a measured 0f the gr p Columbillm, tanta um and Vanadium is presamount of nitrogen and allowing the nitrogen content to be cut the maximum total content, in terms of weight perreduced during treatment as a result of the specimens abcent of such metals must be equal to or less than the sorbing the available nitrogen. For example, total of 7 85(Ratio A)+88(Ratio B)+90(Ratio C) and the minimum content thereof when tungsten and/or molybdenum are present must be equal to or greater than the total of [(Ratio A)+(Ratio B)] [(Ratio E)+25(Ratio D)]+(Ratio C) Furthermore, when there is more than 1 metal of the group columbium, tantalum and vanadium present the maximum amount of titanium permitted in the alloy system is equal to or less than the amount determined by the formula 45(Ratio A+Ratio C) +35(Ratio B) and the ratio of the content of such metals to the titanium must be greater than the ratio determined by Ratio A+Ratio B-|-0.66(Ratio C) :1

Additionally, when both tungsten and molybdenum are present the maximum amount thereof is determined by the formula 60(Ratio A+Ratio C)(Ratio D) +50 (Ratio B) (Ratio D)+80(Ratio B) We would further note that when columbium alone is used of Group A metals and both molybdenum and tungsten are present the minimum amount of columbium required is determined by the formula 10(Ratio E)+(Ratio D) Microhardness (DPN) at depth (mils):

A strip specimen 72 mils thick was prepared using the same titanizing and nitriding procedures and was subsequently bent 45. Cracking of the hard nitrided case occurred on the tension (outer) side. The adherency of the hard nitrided 6 mil zone was shown by the fact that none of it spalled from the Ta-IOW substrate which was intact.

Another surface alloying procedure involved the combined titanizing and vanadizing of molybdenum or tungsten. This can be accomplished by vacuum pack treatment since titanium and vanadium have similar vapor pressures. Such treatment of molybdenum or tungsten at 295 0 F. for 3 hours yields a thinner diffusion zone than that observed for the titanizing of Ob-lSMo. The depth of the dilfusion zone was about 1% mils with molybdenum and less with tungsten. After nitriding at 3250 F. for 2 hours the microhardness of the molybdenum sample was 1000, 605, and 190 DPN at 0.5, 1, and 2 mils, respectively.

Use of surface alloying or coating techniques can enhance the utility of powder processing of the alloys prior to nitriding in a number of ways. For example, a powder processed alloy of Cb-Mo could be formed and then titanized or a porous molybdenum or tungsten presintered compact could be infiltrated by coating methods. These and other techniques can 1) lower sintering temperatures, (2) enhance filling of pores, and (3) reduce shrink- 8 age as compared to making a homogeneous powder part.

We have modified our nitrided material by combining nitriding with oxidizing or boronizing. However, the amount of reaction with such other hardening agents must be limited, a majority of the Weight pick-up is due to nitriding, and these are essentially nitrided materials. The alloys may be preoxidized at a temperature where little reaction would occur with nitrogen alone and then subsequently nitrided. Also, the alloys may be reacted with a combined oxidizing and nitriding environment although the relative oxidizing potential must be low since for example in air the alloys will preferentially oxidize rather than nitride. A sample of Cb-30Ti-20W was nitrided at 3250 F. for 2 hours and subsequently boronized at 2650 F. for 4 hours. The structural features of such a material are very similar to the alloy only nitrided; the hardness grades inwardly and of the total weight pick-up over is due to nitriding. A smooth surface layer about 0.4 mil thick forms due to the boronizing treatment that is harder than the nitrided surface.

For comparison, the Cb-30Ti-20W alloy nitrided at 3250 F. for 2 hours exhibits a microhardness of 2680 DPN at a distance of mil from the surface. After the subsequent boronizing treatment, the hardness was 4550 DPN at the same depth. This duplex treated material passes our test at 750 and SFM but the chipping propensity is increased. Up to 25% of the nitrogen pickup by weight may be replaced by oxygen and/or boron.

Although the alloys receptive to nitriding can be produced by coating or surface alloying techniques, many uses involve the forming and machining of a homogeneous alloy or a coated article. One of the advantages in utility of these materials is our ability to form the metallic alloys by cold or hot working and/or to machine (or hone) to shape in the relatively soft condition prior to final nitriding. Only minimal distortion occurs during nitriding and replication of the starting shape and surface finish is excellent. The final surface is reproducible and is controlled by original surface condition, alloy composition, and nitriding treatment. For some applications, the utility would be enhanced by lapping, polishing, or other finishing operations after nitriding. The nitrided surface is quite hard but only a small amount of material removal is required to produce a highly finished surface.

One of the nitrided effects that we have noticed is an accentuation of sharp edges. Similar to the established technology for aluminum oxide ceramic insert tools, we have blunted sharp cutting edges prior to nitriding. This has been accomplished by simple tumbling prior to nitriding or by finishing subsequent to nitriding. High speed cutting performance will not be degraded if such edge preparation is limited. The nitrided material can be used as a mechanically locked insert or it can be bonded or joined by brazing, for example, to a substrate.

We have also observed the excellent corrosion resistance of both the alloys and the nitrided alloys in strong acids, and these materials could effectively be employed for applications requiring both corrosion and abrasion resistance. Both the alloys and the nitrided alloys possess good structural strength. Thus, the materials can be employed for applications involving wear resistance and structural properties (hardness, strength, stiffness, toughness) at room and elevated temperatures. Other useful properties of the nitrided materials include good electrical and thermal conductivity, high melting temperature, and thermal shock resistance.

The excellent cutting properties and wear resistance of the nitrided materials can be effectively employed with the other useful properties of the alloys and nitrided materials to produce a wide range of products. Some of these are: single point cutting tools, multiple point cutting tools (including rotary burrs, files, routers and saws), drills, taps, punches, dies for extrusion, drawing, and other forming operations, armor, gun barrel liners, impeller of fan blades, EDP (Electrical Discharge Machining) electrodes, spinnerets, guides (thread, wire, and other), knives, razor blades, scrapers, slitters, shears, forming rolls, grinding media, pulverizing hammers and rolls, capstans, needles, gages (thread, plug, and ring), bearings and bushings, pivots, nozzles, cylinder liners, tire studs, pump parts, mechanical seals such as rotary seals and valve components, engine components, brake plates, screens, feed screws, sprockets and chains, specialized electrical contacts, fluid protections tubes, crucibles, molds and casting dies, and a variety of parts used in corrosion-abrasion environments in the papermaking or petrochemical industries, for example.

It will be understood that various modifications and variations may be affected without departing from the spirit or scope of the novel concepts of our invention.

We claim as our invention:

1. Graded, nitrided ternary or higher alloyed material consisting essentially of: at least one metal selected from each of the Groups A, B, and C wherein Group A con-\ sists of columbium, tantalum and vanadium; Group B is titanium and Group C consists of molybdenum and tungsten and wherein:

(a) the nitrogen pickup ranges from 0.1 to less than 1.0 milligram per square centimeter of surface area; (b) when only columbium and molybdenum are present with titanium the range for the columbium content is from about 20 percent to 85 percent; (c) when only columbium and tungsten are present with titanium the range for the columbium content is from about 10 percent to 85 percent;

(d) when only columbium, molybdenum and tungsten are present with titanium the minimum amount of columbium required is determined by the formula 10(Ratio E)+20(-Ratio D) and the maximum content of columbium is about 85 percent;

(e) when only tantalum and molybdenum are present with titanium the range for the tantalum content is from about 25 percent to 88 percent;

(if) when only tantalum and tungsten are present with titanium the range for the tantalum content is about 10 percent to 88 percent;

(g) when only tantalum, molybdenum and tungsten are present with titanium the minimum amount of tantalum required is determined by the formula l(Ratio E) +25 (Ratio D) and the maximum content of tantalum is about 88 percent;

(h) when only vanadium and a metal selected from the group consisting of molybdenum and tungsten and combinations thereof are present with titanium the range for the vanadium content is about 15 percent to 90 percent;

(i)when more than one metal of the group columbium,

tantalum and vanadium are present with only molybdenum and titanium the minimum total content of the metals columbium, tantalum and vanadium must be at least equal to the amount of 20(Ratio A) +25(Ratio B)+15(Ratio C) (j) when more than one metal of the group columbium, tantalum and vanadium are present with only tungsten and titanium, the minimum total content of the metals columbium, tantalum and vanadium must be at least equal to the amount of (Ratio A)+10(Ratio B)+(Ratio C) (k) when more than one metal of the group columbium, tantalum and vanadium are present with molybdenum, tungsten and titanium, the minimum total content of the metals columbium, tantalum and vanadium must be at least equal to the amount of [(Ratio A)+(-Ratio B)] [10(-Ratio E)+25 (Ratio D)]+15(Ratio C) 10 (1) when more than one metal of the group columbium, tantalum and vanadium are present the maximum total content thereof must be equal to or less than (Ratio A)+88(Ratio B)+90(-Ratio C) (in) when titanium is present with only columbium and a metal selected from the group molybdenum and tungsten and combinations thereof, the titanium content ranges from about 1 percent to 45 percent and the columbium to titanium ratio is greater than (n) when titanium is present with only tantalum and a metal selected from the group molybdenum and tungsten and combinations thereof, the titanium content ranges from about 1 percent to 35 percent and the tantalum to titanium ratio is greater than 1;

(0) when titanium is present only with vanadium and a metal selected from the group molybdenum and tungsten and combinations thereof, the titanium content content ranges from about 1 percent to 45 percent and the vanadium to titanium ratio is greater than 0.66;

(p) when titanium is present with more than one metal of the group columbium, tantalum and vanadium and a metal selected from the group molybdenum and tungsten and combinations thereof, the maximum content of titanium must be equal to or less than 45(Rati0 A+Ratio C) +35(Ratio B) and the ratio of the content of the metals columbium, tantalum and vanadium to titanium must be equal to or greater than the ratio of (Ratio A)+(Ratio B)+0.66(-Ratio C):1

and the minimum titanium content is 1 percent;

(q) when only molybdenum, titanium and a metal selected from group columbium and vanadium and combinations thereof are present, the range for molybdenum content is from about 2 percent to 60 percent;

(r) when only molybdenum, titanium and tantalum are present the range of the molybdenum content is from about 2 percent to 50 percent;

(s) when only tungsten, titanium and a metal selected from the group columbium, tantalum and vanadium and combinations thereof are present the range for tungsten content is from about 2 percent to 80 percent;

(t) when molybdenum, tungsten, titanium and a metal selected from the group columbium, tantalum, vanadium and combinations thereof are present the maximum total content of molybdenum and tungsten must be equal to or less than 60(Ratio A+Ratio C) (Ratio D-)+50 (Ratio B)(Ratio D)+80(Ratio E) and the minimum content of molybdenum and tungsten is 2 percent; (u) and wherein in the foregoing 11 12 2. The material as defined by claim 1 wherein up 3,173,7-84 3/1965 Weodek et a1. 75174 to 3 percent of the titanium content is replaced by 3,471,342 10/1969 Wood 14831.5

zirconium.

References Cited UNITED OTHER REFERENCES 5 IR 718-7 (III), lIT Research, June 16, 1967--Sept.

STATES PATENTS 15, 1967, pp. 51-55, 59, 60, 65 and 67.

A st 143-403 E E, X CHARLES N. LOVELL, Primary Examiner Van Note 14820.3

Berger et a1. 75-177 10 CL Lenning et a1 75-174 29182.2, 182.5; 14s 20.3

Douglass et a1. 148-34