RESISTORS FORMED OF ALUMINUM-TITANIUM ALLOYS

Abstract: Resistors for use in electrical circuits are formed of an alloy comprising from about 50 to about 95 mol percent aluminum, from about 5 to about 50 mol percent titanium and up to about 15 mol percent of at least one additional metal or a combination of two or more additional metals.

Description: RESISTORS FORMED OF ALUMINUM-TITANIUM ALLOYS FIELD OF THE INVENTION The present invention relates to resistors adapted for use in electrical circuits and formed of aluminum-titanium alloys. BACKGROUND OF THE INVENTION Heavy duty power resistors are commonly employed in electrical circuits to control electrical current flow by converting electrical energy to heat, which may then be dissipated into the surrounding environment. Normally, resistors rated at 300 watts and above are considered power resistors. Typically, power resistors have been made from nickel-chromium alloys (NiChromes), copper-nickel alloys (Cu-Ni) or stainless steel alloys, with FeCrAl, 304 and 430 being the most common stainless steel types. Stainless steel is often modified with additional metals to improve its electrical characteristics, for example, resistivity and changes in resistivity levels over an operating temperature range. While all of these materials may be used in high temperature applications, i.e. up to about 1000°C, they all have one or more shortcomings which compromise their use. For example, the nickel-chromium alloys commonly referred to NiChrome materials are expensive and heavy, both of which factors limit their use in a wide range of applications. On the other hand, the copper-nickel alloys are expensive and exhibit relatively low working temperatures and melting points. Additionally, the copper-nickel alloys are disadvantageous in that they are not readily available in sheet form. The stainless steel alloys also exhibit a relatively low resistivity and typically the resistivities of these alloys vary substantially over a temperature range, thereby rendering the alloys unsuitable for applications requiring precise resistivity requirements. Additionally, the type 430 stainless steel which is commonly employed is slightly magnetic and therefore unsuitable for low inductance applications. Various modified forms of stainless steel are also slightly magnetic and therefore unsuitable for low inductance applications. These modified stainless steel alloys are also typically more expensive and therefore not attractive for widespread use. Accordingly, there is a continuing need for new resistors which would be suitable for widespread use, and particularly in heavy duty environments. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide new resistors which may be advantageously employed in various applications owing to a desirable combination of properties. It is a further object of the invention to provide nonmagnetic and lightweight resistors. It is a related object to provide such resistors which can be rated at 10 watts and above and which may be employed in heavy duty power environments. It is another object to provide resistors which may be employed in high temperature applications and in a temperature range of -40 to 1200°C. These and additional objects are satisfied by the present invention which is directed to resistors adapted for use in electrical circuits. The resistors are formed of an alloy comprising from about 50 to 95 mol percent aluminum, from about 5 to about 50 mol percent titanium and up to about 15 mol percent of at least one additional metal or a combination of two or more additional metals. The resistors according to the present invention are strong, lightweight and non-magnetic. Additionally, the resistors according to the present invention exhibit nearly constant resistivity over a wide operating temperature range. The alloys from which the resistors are formed exhibit a good combination of ductility, material density and melting point to allow efficient manufacture of the resistors. These and additional objects and advantages provided by the present invention will be more fully understood in view of the following detailed description. BRIEF DESCRIPTION OF THE DRAWING The Figure sets forth resistivity measurements for various resistors according to the present invention over a temperature range of from about 25 °C to 600°C, as described in further detail herein. DETAILED DESCRIPTION The resistors according to the present invention are adapted for use in an electrical circuit and may be formed of any conventional resistor structure. As known in the art, resistors are employed to control current flow in an electrical circuit. Preferably, the resistor will include connectors for facilitating connection of the resistor into an electrical circuit in a conventional manner. The resistors of the present invention are suitable for use in a variety of applications, including heavy duty environments requiring resistors rated at 10 watts and above. The resistors according to the present invention are formed of an alloy which comprises from about 50 to about 95 mol percent aluminum, from about 5 to about 50 mol percent titanium and up to about 15 mol percent of at least one additional metal or a combination of additional metals. The present inventors have discovered that the aluminum-titanium alloys from which the present resistors are formed provide lightweight yet strong resistors. Additionally, the combination of ductility, resistivity, density and melting point exhibited by these alloys facilitates formation of the alloys into resistors of desired shapes and sizes, particularly when the alloys comprise at least one additional metal or a combination of additional metals in an amount up to about 15 mol percent. Additionally, the alloys from which the present resistors are formed exhibit good corrosion resistance without disadvantageous^ effecting the resistivity properties. In a preferred embodiment, the resistors according to the present invention are formed of an alloy comprising from about 60 to about 90 mol percent aluminum, or more preferably from about 60 to about 80 mol percent aluminum, from about 5 to about 30 mol percent titanium and from about 5 to about 15 mol percent of at least one additional metal. In a further preferred embodiment, the resistors according to the present invention are formed from an alloy comprising from about 65 to about 70 mol percent aluminum, from about 20 to about 30 mol percent titanium and from about 5 to about 10 mol percent of at least one additional metal. In one embodiment, the at least one additional metal comprises one or more transition metals of groups IB-VIIB or group VIII, although other metals, for example, boron, may be employed, alone or in combination with one or more transition metals. In a preferred embodiment, the additional metal is selected from the group consisting of copper, manganese, iron, chromium, vanadium, nickel, boron, and mixtures thereof. Generally, the alloys according to the invention exhibit densities in the range of from about 3.35 to about 4 g/cm 3 . These alloys have melting points greater than 1200°C, which facilitate their use in high temperature environments. The alloys from which the resistors of the present invention are formed may themselves be formed in accordance with conventional metal alloying techniques. Additionally, the alloys may be formed to resistors in accordance with techniques known in the art and particularly processing such as annealing, pressing, cutting, drilling and the like are facilitated with the alloys according to the present invention, particularly wherein at least one additional metal is included in the aluminum-titanium alloy. The resistors according to the present invention are demonstrated in further detail in the following example. In the example and throughout the present specification, parts and percentages are on a molar basis unless otherwise specified. Example In this example, various aluminum-titanium alloys are formed and subjected to measurement of Vickers hardness according to ASTM-E92 using a load of 200 gf. The approximate molar composition and hardness of each alloy is set forth in Table 1. The hardness value for each allow is presented as an average of six measured values. TABLE 1 The alloys were formed as resistors, inserted into an electrical circuit and subjected to measurement of resistivity over a temperature range of from ambient to about 600°C according to the four probe technique known in the art. The area and length of each resistor sample subjected to measurement is set forth in Table 2, and the results of the resistivity measurements are set forth in the Figure. The Figure also sets forth the resistivity measurements of a standard resistor formed of stainless steel SS2C. TABLE 2 The results set forth in the Figure demonstrate that resistors according to the present invention generally exhibit consistent resistivity over wide temperature ranges and at a variety of levels, thereby demonstrating that the resistors according to the present invention are suitable for use in a variety of applications, including precision applications wherein significant variations in resistivity are to be avoided. Preferably, the resistivities according to the invention vary by not more than about 50%, more preferably by not more than about 30%, and even more preferably by not more than about 10%), over a temperature range of from about 25°C to about 600°C. Additionally, the non-magnetic, lightweight, corrosion resistance and strength characteristics of the resistors according to the present invention contribute to their advantageous use in a variety of applications. The specific embodiments and examples set forth herein are provided to illustrate various embodiments of the invention and are not intended to be limiting thereof. Additional embodiments within the scope of the present claims will be apparent to one of ordinary skill in the art.

Claims: What is claimed is: 1. A resistor adapted for use in an electrical circuit and formed of an alloy comprising from about 50 to about 95 mol percent aluminum, from about 5 to about 50 mol percent titanium, and up to about 15 mol percent of at least one additional metal. 2. A resistor as defined by claim 1 , formed of an alloy comprising from about 60 to about 80 mol percent aluminum, from about 5 to about 30 mol percent titanium, and from about 5 to about 15 mol percent of at least one additional metal. 3. A resistor as defined by claim 2, wherein the additional metal comprises a transition metal. 4. A resistor as defined by claim 2, formed of an alloy comprising from about 65 to about 70 mol percent aluminum, from about 20 to about 30 mol percent titanium, and from about 5 to about 10 mol percent of at least one additional metal. 5. A resistor as defined by claim 4, wherein the additional metal is selected from the group consisting of copper, manganese, iron, chromium, vanadium, nickel, boron, and mixtures thereof. 6. A resistor as defined by claim 1, formed of an alloy consisting essentially of aluminum, titanium and an additional metal selected from the group consisting of copper, manganese, iron, chromium, vanadium, nickel, boron, and mixtures thereof. 7. A resistor as defined by claim 1 , formed of an alloy consisting of aluminum and titanium. 8. A resistor as defined by claim 1, formed of a material of the approximate molar composition Al 063 Cuo 12 Ti 025 . 9. A resistor as defined by claim 1, formed of a material of the approximate molar composition Al^Mn^sT^. 10. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 067 Fe 008 Ti 025 . 11. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 06g B 007 Ti 025 . 12. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 067 Cr 008 Ti 025 . 13. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 067 V 008 Ti 025 . 14. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 067 Ni 008 Ti 025 . 15. A resistor as defined by claim 1 , formed of a material of the approximate molar composition Al 079 Ni 0 M Ti 007 . 16. A resistor as defined by claim 1 , adapted for operation over a temperature range of from ambient up to about 600 °C. 17. An electrical circuit, comprising a current source and at least one resistor formed of an alloy comprising from about 50 to about 95 mol percent aluminum, from about 5 to about 50 mol percent titanium and up to about 15 mol percent of at least one additional metal. 18. An electrical circuit as defined by claim 17, wherein the resistor is formed of an alloy comprising from about 60 to about 80 mol percent aluminum, from about 5 to about 30 mol percent titanium and from about 5 to about 15 mol percent of at least one additional metal. 19. An electrical circuit as defined by claim 18, wherein the additional metal is selected from the group consisting of copper, manganese, iron, chromium, vanadium, nickel, boron, and mixtures thereof. 20. A method of controlling current flow in an electrical circuit, comprising including in the electrical circuit a resistor formed of an alloy comprising from about 50 to about 95 mol percent aluminum, from about 5 to about 50 mol percent titanium and up to about 15 mol percent of at least one additional metal.

Inventors: BERGER ROBERT E II, KUMAR BINOD, BERGER, ROBERT, E., II, KUMAR, BINOD
Applicants: BERGER ROBERT E II, KUMAR BINOD, POST GLOVER RESISTORS INC, BERGER, ROBERT, E., II, KUMAR, BINOD, POST GLOVER RESISTORS INC.
Application year: 1998
Main classification: H01C3
IPC codes: H01C3, H01C7