Patent Application
20080031766
This invention relates to a process whereby titanium and titanium alloy powders produced by the Armstrong process are inertly attrited to increase the apparent density, tap density and packing fraction while maintaining the powder chemistry for further processing to obtain high quality consolidated material.
The powder of the invention is produced by the Armstrong Process as previously disclosed in U.S. Pat. Nos. 5,779,761, 5,958,106 and 6,409,797, the entire disclosures of which are herein incorporated by reference.
Production of titanium powder by the Armstrong Process inherently produces agglomerated ligmental powder in which the average diameter of individual particles is less than five microns with a packing fraction in the range of from about 4% to about 11%. Tap density is defined as the mass of a material that, upon packing in a precisely specified manner, fills a container to a specified volume, divided by the container volume. Apparent density is defined as the weight per unit volume of a metal powder, in contrast to the weight per unit volume of the individual particles. Packing fraction percentage is the tap density divided by the theoretical density and multiplied by 100.
Many projected powder metallurgy uses of titanium and titanium alloy powders require a apparent density or packing fraction higher than the powder typically produced by the Armstrong Process. Increasing the apparent density or packing fraction of the powders produced by the Armstrong Process without significantly increasing oxygen concentration is important to future commercial success in the powder metallurgy field. Powder metallurgy processes include consolidation, molding and also several direct powder to mill shape processes such as powder extrusion and powder roll compaction.
Accordingly, a principal object of the present invention is to provide a titanium or titanium alloy powder having apparent densities and packing fractions greater than powder produced by the subsurface reduction of titanium tetrachloride vapor or mixtures of halide vapors in a flowing stream of alkali or alkaline earth metal or mixtures thereof.
Another object of the present invention is to provide powder with increased apparent density or packing fraction without significantly increasing the oxygen concentration or other contamination above as-produced powder.
Yet another objection of the present invention is to provide a method of increasing the apparent density of agglomerated ligmental titanium or titanium alloy powder produced by the subsurface reduction of titanium tetrachloride vapor or a mixture of titanium tetrachloride and other halide vapors in a flowing stream of alkali or alkaline earth metal or mixtures thereof having a first apparent density after distillation, comprising introducing the agglomerated ligmental titanium or titanium alloy powder into an attriting system, attriting the agglomerated ligmental titanium or titanium alloy powder until the powder becomes more spherical than ligmental and the first apparent density is increased by a factor of from about 3 to about 8.
Still another object of the present invention is to provide a method of increasing the apparent density of agglomerated ligmental titanium or titanium alloy powder produced by the subsurface reduction of titanium tetrachloride vapor or a mixture of titanium tetrachloride and other halide vapors in a flowing stream of sodium or alkaline earth metal or mixtures thereof having a first apparent density after distillation, comprising introducing the agglomerated ligmental titanium or titanium alloy powder into an attriting system, attriting the agglomerated ligmental titanium or titanium alloy powder in an inert atmosphere until the powder becomes more spherical than ligmental and the first apparent density is increased by a factor of from about 3 to about 8.
A final object of the present invention is to provide a method of increasing the apparent density of agglomerated ligmental titanium or titanium alloy powder produced by the subsurface reduction of titanium tetrachloride vapor or a mixture of titanium tetrachloride and other chloride vapors in a flowing stream of sodium or alkaline earth metal or mixtures thereof having a first apparent density after distillation, comprising introducing the agglomerated ligmental titanium or titanium alloy powder into an attriting system including a jet mill, attriting the agglomerated ligmental titanium or titanium alloy powder in an inert atmosphere in the jet mill until the powder becomes more spherical than ligmental and the first apparent density is increased by a factor of from about 3 to about 8.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated.
FIGS. 4(a) and 4(b) are SEMs of agglomerated ligmental titanium powder after milling with an apparent density of 1.13 g/cc;
FIGS. 5(a) and 5(b) are SEMs of agglomerated ligmental titanium powder after milling with an apparent density of 0.82 g/cc;
FIGS. 7(a)-(b) are SEMs of agglomerated ligmental titanium powder after milling with an apparent density of 1.12 g/cc; and
Referring to
A variety of different mechanisms may be used to attritte powder such as but not limited to a ball mill, a jet mill, a high pressure water mill, a mechanco-fusion mill or a hammer mill all of which are included in the invention. A jet mill is illustrated in
The milling of the titanium powder was done on two different Micron-Master jet mills, which are manufactured by the Jet Pulverizer Company. The powder was fed into the mill through a rotating screw conveyor. From that conveyor, the powder flowed into the mill. The compressed nitrogen entered the mill through two nuzzles and the two streams met together in the main chamber of the mill, where the actual milling takes place, as seen in
Three different batches of titanium powder were used to perform the attrition study. Batch R20.13, R20.14, and R20.15 was milled on an 8 inch mill to develop the appropriate jet milling parameters for the desired apparent density. Those parameters were subsequently used to scale up to an 12″ but a 24″ jet mill or larger could be employed. Table 1 summarizes the results from an 8″ mill test. Pre-sieving of the titanium powder was necessary in order to feed the powder into an 8″ mill, which can be eliminated by using a larger mill.
The feed rates and pressures determined from jet milling the powder on an 8″ mill were used to directly feed batch R19.28, R19.29, R22.23, and R22.24 into a 12″ mill. The parameters used for a 12″ mill are shown in Table 2.
The attrition study concentrated on improving the apparent density of the Armstrong Process powder while minimizing the subsequent oxygen pick up resulting from the jet milling process. The purpose for improving the powder density was to make Armstrong powder more amenable to standard powder metallurgy practices. Typically, densities greater than 20% are desired. Based on previous small scale milling experience with Armstrong powder, ITP selected an opposed jet mill as the means to accomplish the attrition. Summary of results for the attrition study is shown in Table 3.
Scotts biometric density meter was used to determine the attrited batch sample's apparent densities and all samples showed considerable improvement. The apparent densities ranged from approximately 6% for raw powder to 25% for milled powder. The particle size analysis was preformed using Coulter LS 230 and showed as expected a decrease in particle size as the apparent density increased across all samples. Inert gas fusion method was used to conduct the chemical analysis for oxygen, nitrogen, and hydrogen. The results showed an increase in oxygen level with dissimilar amounts for different samples. The large increase in oxygen could have resulted from not having a closed system during the milling process. Therefore, to optimize the milling process an inert feeding chamber and completing closed mill might minimize the oxygen increase. The hydrogen level was virtually unchanged during the milling process. Nitrogen level for the powder samples after attrition did increase to some extent, but not enough to cause any problems in further processing of the powder. Scanning Electron Microscope (SEM) was used to evaluate the influence of jet milling on titanium powder particles. SEM's of batch samples R19 and R22 are shown in FIGS. 3,4(a)(b), 5(a)-(b), 6, 7 (a)-(b) and 8(a)-(b). The SEM's showed agglomerated ligmental that as the apparent density increased, the particles became more spherical in shape, which improved the apparent and tap densities.
Table 4 shows additional results using 4 and 8 inch mills such as illustrated in
For certain powder metallurgy, tap densities between about 20% to about 30% are preferred, but as illustrated in Tables 1-4, packing fractions of as produced powders (inherently in the range of from about 4% to about 11%) may be increased to at least 45%, see particularly Table 4. The jet mills were operated at various feed rates in pounds per hour (lb./hr) and at various pressures in pounds per square inch (psi). Pressure as low as 30 psi (Table 1) or up to 130 psi (Table 4) have been used and feed rates from 5 to 110 lbs/hr. have been used (Tables 1 and 4). Pressures and feed rates affect the increase in apparent density, tap density and packing fraction.
While there has been disclosed what is considered to be the preferred embodiment of the present invention, it is understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
This application, pursuant to 37 C.F.R. 1.78(c), claims priority based on provisional application U.S. Provisional Application Ser. No. 60/814,362 filed Jun. 16, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60814362 | Jun 2006 | US |
