1. Field of the Invention
This invention relates to a nickel-base alloy which resists corrosion, abrasion, erosion, cavitation and temperature cycles and possesses a high-temperature strength. In particular, this invention relates to an improved alloy of the type disclosed in corresponding application Ser. No. 828,718 which alloy has the following composition in percent by weight:
Carbon: 0.5 to 5 PA1 Tungsten: 2 to 15 PA1 Chromium: 25 to 55 PA1 Boron: 0.5 to 3.5 PA1 Silicon: 1 to 5 PA1 Iron: 1 to 5 PA1 Nickel: balance PA1 (a) percent by weight C=percent by weight C.sub.1 +percent by weight C.sub.2 +0.2; PA1 (b) percent by weight W=36.times.percent by weight C.sub.1 ; and PA1 (c) percent by weight Cr.gtoreq.17+9.times.percent by weight-4.times. PA1 percent by weight C.sub.1 =carbon content required to form carbides with refractory metals (tungsten, molybdenum) PA1 percent by weight C.sub.2 =carbon content required to form chromium carbide PA1 0.2=a constant which is equivalent to the solubility limit of C in the nickel-chromium solid solution.
and meet the following boundary conditions:
Where:
In particular this invention relates to such an alloy additonally containing phosphorus, e.g., in an amount of 0.5-4.5 weight percent. The alloy has improved processing characteristics.
2. Discussion of the Prior Art
In virtually all fields of industrial activity, it is desired to solve problems relating to the wear and corrosion of highly stressed components by coating them with hard alloys so as to save raw material. Hard alloys based on cobalt and nickel have been used for decades with success particularly in the manufacture of machines, equipment and fittings.
In nuclear engineering the use of cobalt alloys, so-called stellites, is limited by the presence of cobalt. For this reason it has been attempted most recently to replace stellites by nickel-chromium-boron-silicon hard alloys, which can also be processed in a simpler manner. On the other hand, it has been found that boride- and silicide-containing hard nickel alloys are not satisfactory with respect to their resistance to corrosion, particularly intergranular corrosion. In many cases, nickel-chromium-boron-silicon alloys are unsatisfactory also in respect of high-temperature strength and susceptibility to cracking. For this reason, a new type of nickel-containing hard alloy has been developed and disclosed in corresponding application Ser. No 828,718, filed Aug. 29, 1977, entitled: "Nickel-Base Alloy", assigned to the assignee hereof, the disclosure of which is hereby incorporated specifically herein by reference.
In view of their characteristic content of hard material, these coating alloys are described as carbide-content of the alloy in adaptation to the relatively high chromium and tungsten contents and additions of boron, silicon and iron permit of a production of hard alloys having a hardness in the range of 35 to 50 to HRC and a high resistance to corrosion.
The new hard aloys have the structure which is typical of hard alloys. The hard material phases which are responsible for the wear resistance are embedded in a regular distribution in a relatively ductile metal matrix. In dependence on the alloy constituents and their mutual solubility in the solid state, the metal matrix consists of a solid solution of nickel, which contains chromium, tungsten, silicon, carbon and iron. The predominant hard material phase consists of a complex carbide of the type M.sub.7 C.sub.3, wherein M stands for the metals chromium, nickel and tungsten. Owing to the extremely low solubility of boron in the matrix solid solution, another hard phase consists of chromium borides, mostly of the type CrB. Depending on the proportions of the alloying constituents within the stated tolerance ranges and the cooling conditions adopted in the production and processing of the alloy, additional hard phases may be stabilized in small quantities, if desired. They consist of the complex carbides of types M.sub.23 C.sub.6 and M.sub.2 C and a silicon-stabilized carbide of the type M.sub.6 C.
The new alloys afford advantages regarding the resistance to abrasion at higher temperatures because alloys having a comparatively smaller hardness at room temperature can be used so that the processing and machining will be facilitated.
In addition to its high strength at room temperature, the alloy distinguishes by an excellent strength at high temperature and an almost constant strength at temperatures in the range of 300.degree. to 600.degree. C.
As regards thermal expansion and density, the novel hard nickel alloys are comparable to corresponding conventional hard alloys based on nickel or cobalt.
In addition to their good mechanical properties, carbide-containing hard nickel alloys exhibit also a favorable melting behavior. The melting temperature range of about 1170.degree. to 1230.degree. C. is lower than that of comparable hard cobalt alloys. This results in excellent processing characteristics.
Owing to their excellent resistance to corrosion, the novel hard alloys close a gap which has existed in the conventional hard nickel alloys, which have an extremely poor resistance particularly to oxidizing media.