Molybdenum nickel chromium bonded titanium carbide
United States Patent Humenik, Jr. et al.  
 [ Apr. 22, 1975 MOLYBDENUM NICI (EL CHROMIUM BONDED TITANIUM CARBIDE Inventors: Michael IIumenik, Jr., Allen Park: David Moskowitz, Southfield. both of Mich.  
 Ford Motor Company, Dearborn. Mich.  
 Filed: Dec. 22, 1971 Appl. No.: 210,657  
 Assignee:  
 US. Cl 29/95 D; 29/95 A; 29/182.7 Int. Cl. B26d 1/00 Field of Search 82/1 C; 29/l82.7, 95 A,  
 References Cited UNITED STATES PATENTS Kelly et a1 Q9/1827 X 3.480.410 11/1969 Hummer 29/l82.7  
 3,507,631 4/1970 Yates 29/18&#39; 7 3.551991 1/1971 Reich et 29/l82.8 X 3,552.93? l/l971 Mito et al. Q9/1827 Primary Examiner- Leonidas Vlachos -Al!urney, Agenl. 0r Firm-Joseph W. Malleck; Keith L. Zerschling [57] ABSTRACT 3 Claims, 3 Drawing Figures FIG FIG  
 FIG  
 MOLYBDENUM NICKEL CHROMIUM BONDED TITANIUM CARBIDE HISTORICALLY Metal cutting bits in which the hard material is titanium carbide and the bonding metal an alloy of molybdenum and nickel have long been known to the machining fraternity and have enjoyed considerable commerical success. These titanium carbide based bits have replaced to a substantial extent the tungsten carbide bits which for decades dominated the high speed machining field.  
  These titanium carbide cutting bits have given generally very satisfactory commerical service and for many purposes result in lower cutting costs than other com petitive materials. Carbide cutting tools tend to fail in roughing or intermittent cuts by a mechanism known as thermal fatigue or thermal cracking. This invention teaches a system by which these premature failures due to thermal fatigue or thermal cracking may be largely avoided.  
 THE INVENTION This invention is predicated upon the fact that the thermal performance of titanium carbide cutting tools can be enormously improved by substituting chromium for a portion of the nickel in the nickel molybdenum binding alloy. Optimum results have been obtained by replacing between 40 and I percent of the nickel in the bonding alloy by chromium. The chromium will be added to the powder mix before compaction and may be added as elemental chromium. chromium carbide. a solid solution of chromium carbide in titanium carbide. a nickel alloy. or any mixture of these sources of chromium.  
  A typical cutting tool produced by this invention comprises 22:5 percent nickel. 10.0 percent molybdenum. five percent chromium with the remainder titanium carbide and incidental impurities. The binding alloys were added as approximately five micron powder. A titanium carbide powder composition having the following analysis was chosen as the base material:  
 Free carbon .2 I &#34;/1 Combined carbon l 9.5; Titanium 79.3 Oxygen 19% The size analysis of this material as determined by Fisher particle size analysis was 3.67 microns.  
  The particle size distribution. using the Turbidimeter method of analysis. was as follows:  
 0-5 microns 46.4 weight /2 -H! microns 27.3 weight 71 IU-Zt) microns 26.4 weight &#34;/1 The grinding operations were conducted in a Hastelloy B mill containing titanium carbide base balls. acetone being added to inhibit oxidation ofthe charge during the 96 hour milling period. After milling the acetone was evaporated and four percent wax binder was added. Upon drying the powder was pressed in a steel die at a pressure of about l0 tons per square inch.  
  The cold pressed compacts were presintered in a hydrogen ambient at l.2()0 Fahrenheit for 1 hour to dewax the specimens. Final sintering was performed on an inert stool and in an inert ambient at 2.500 Fahrenheit for l hour in an induction furnace. An absolute pressure of about 0.] to 1.0 microns was maintained in the furnace although any suitable inert ambient will be satisfactory. Additional suitable inert ambients are dry hydrogen. argon or helium. The sintering temperature is. of course. a function of sintering time. the time being shortened as the temperature is raised. In any event the sintering temperature should not exceed 2.700 Fahrenheit to avoid substantial grain growth. The time and temperature of sintering must be adjusted so that the grain size of the titanium carbide in the finished article is not substantially larger than approximately five microns.  
  It is essential that the initial binding alloy contain at least 10 percent of molybdenum to take advantage of the ability of this metal to cause alloys containing it to wet the surface of the hard titanium carbide particles.  
  The titanium carbide employed in these cutting tools prior to sintering should be effectively free of molybdenum carbides in solid solution.  
  Since the sintering temperatures employed in the preparation of the compacts are high enough to permit the constituents of the compacts to come to equilibrium between the titanium. molybdenum and carbon. it would appear at first blush to be immaterial whether the molybdenum were added as elemental molybdenum. as molybdenum carbide. or as a solid solution of molybdenum carbide in titanium carbide. However. experience has demonstrated that the addition of molybdenum as the carbide dissolved in titanium carbide produces decidedly inferior tools while the addition of molybdenum as elemental molybdenum or as molybdenum carbide not dissolved in titanium carbide produces decidedly satisfactory tools.  
  Without being bound by the following seemingly correct explanation of the superior performance of the tools of the current invention. the mechanism of the improvement appears to be as follows. The performance of these modified tools is particularly improved in making roughing or intermittent cuts where the actual cutting edge of the tool is rapidly and intermittently heated and cooled. These thermal excursions of the cutting tool edge are due to the fact that at least a portion of the cutting edge of the tool is out of actual contact with the work during a. portion of a revolution of the work piece due to casting defects. nonconcentricity of parts of the work piece with the axis of the cutting machine. or cutting across depressions deliberately provided such as key ways.  
  All of the tool edge actually and instantaneously engaged in cutting becomes highly heated by cutting friction. As a portion or all of the cutting edge becomes disengaged momentarily from the work it becomes exposed to the quenching effect of the cutting coolant or the self-quenching effect of the adjacent cool parts of the tool. These repeated thermal excursions of the tool edge cause the metal to expand and cause stress beyond the yield point resulting in permanent deformation or strain. These cumulative repeated plastic deformations of the tool edge result in premature failure of the tool.  
  FIG. 1 of the drawings is a slightly magnified photograph of a conventional titanium carbide cutting tool which has failed by repeated thermal strain. Note the destruction of the working tip of the tool.  
  FIG. 2 also depicts a conventional titanium carbide cutting tool at an earlier stage of failure. Note that this cutting tool exhibits severe thermal cracking and that the cracks are disposed both normal to the cutting edge and parallel to the cutting edge. It is the presence of the cracks parallel to the cutting edge which promotes catastrophic failure of the tool bit. This drawing shows an unmodified titanium base tool containing as bonding metals 17.5 percent nickel and nine percent molybdenum. This particular tool had machined one hundred automotive rear axle pinion gears in a rough turning and facing operation.  
  FIG. 3 shows the crack pattern obtained on the same base composition modified by the presence of chromium. the chromium was present to the extent of percent of the nickel content. This tool was employed in the same machining operation of the rear axle pinion gears and at the same machining operation of the rear axle pinion gears and at the time the photograph was taken had machined two hundred pieces or twice as many as the tool shown in FIG. 2. Attention is especially invited to the fact that in this tool the thermal cracks are oriented only normally to the edge of the cutting tool instead of normal and parallel to the edge as shown in FIG. 2. The tool in FIG. 3 is still in operable condition. The absence of cracks parallel to the edge of the tool makes the decrepitation of the bit much less likely to occur.  
  This is an improvement over the invention described and claimed in Reissue U.S. Pat. No. 25.815 dated Jul. 6. I965 and the teaching thereofis incorporated herein by reference.  
 We claim as our invention:  
  1. An admixture for making a hard sintered metallic cutting tool highly resistant to thermal shock and wear. comprising:  
 a. a base particulate constituent consisting essentially of titanium carbide and being free of detrimental quantities of nitrides and oxides and further being essentially free of dissolved molybdenum. molyb-.  
 denum carbides. chromium. and chromium carbides.  
 b. a binder constituent comprising l0-50 percent of the admixture and consisting essentially ofa particulate having elements selected from the iron group. nickel elemental chromium and molybdenum. said elemental chromium being present in the binder as chromium or chromium carbide compounds or a mixture thereof and being present in a weight amount between 10-40 percent of said nickel. and said molybdenum being present as molybdenum or molybdenum compounds in an amount between 25-70 percent of said nickel.  
  2. An admixture for making a hard sintered metallic cutting tool highly resistant to thermal shock and wear. comprising:  
 a. a base particulate constituent consisting essentially of titanium carbide and being free of detrimental quantities of nitrides and oxides and further being essentially free of dissolved molybdenum and molybdenum carbides.  
 b. a binder constituent comprising 10-50 percent of the admixture and consisting essentially ofa particulate having elemental or combined forms of nickel. chromium and molybdenum. the chromium form being present in the binder in an amount measured as elemental chromium in the range between l0-40 percent of said nickel form. and said molybdenum form being present in an amount between 25-70 percent of said nickel form and said binder.  
  3. A sintered metallic cutting tool as in claim 1. in which said tool is sintered at a temperature not in excess of 2.700 F. thereby maintaining thegrain size of the titanium carbide base material at a size equal to or less than 5 microns.