Suitable Metals

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Ferrous Alloys:

The Borofuse Process can be applied virtually to all ferrous alloys. Core hardness can be controlled independently to achieve the optimum combination of surface and bulk properties. The most suitable base metal for a specific application is determined by a variety of parameters such as depth of boride, core hardness, fabrication procedures, size, and tolerances. Tolerances can be particularly significant in that the Borofuse Process is carried out above tempering temperatures. However, by controlling heat treatment prior to Borofuse Processing and then choosing appropriate thermal conditions for processing, dimensional change can be minimized.

Nickel Alloys

Virtually all nickel alloys respond to the Borofuse Process. Many of the age-hardening alloys, such as Inconel 718, can be processed under conditions compatible with the appropriate aging treatment. For example, Fig. 4 shows Inconel 718 Borofuse Processed at 1400° F, followed by a second aging treatment at 1200° F.

Fig. 4

Borofuse Processed IN718
(360 x)

The fully aged Inconel 718 substrate is Rc42 (425 KHN), whereas the Borofuse Processed surface is approximately 1450 KHN. Additionally, the nickel borides exhibit excellent corrosion properties in many environments. As a consequence, the surface hardness of nickel alloys can be substantially increased for most applications without sacrificing the intrinsic corrosion properties. Further, the intermettalic nickel borides exhibit good hot hardness, and thus can be used in elevated temperature environments. The substantial improvement in wear behavior of Borofuse Processed nickel alloys is demonstrated using the Falex-ISC Pin-on-Disk Wear Test. In this test, both the pin and disk were borided, and the wear was characterized by weight loss. Inconel 718 in the fully aged condition showed a disk weight loss of 10.1 mg, whereas the borided disk exhibited no detectable weight loss (the weight measurement is accurate to +/- .5 mg). Moreover, the non-borided disk exhibited a significant wear scar, including galling, whereas the borided disk displayed only a light polished condition. This test also calculates a volume loss as per the G99 procedure. The volume loss of the Non-Borofuse Processed™ Inconel 718 disk was 100 times that of the Borofuse Processed™ disk, consistent with the weight loss data. Borofuse Processing™ the Inconel 718, therefore, virtually eliminated wear and galling under the test conditions.**Pin-on-Disk, 750 gm. load, non-lubricated, 50 rpm, 1.5” disk wear track diameter, 60 min. test duration.

Metal Bonded Carbides

All grades of cobalt and nickel bonded tungsten and titanium carbides can be treated with the Borofuse Process. The diffused boron converts the relatively soft metal binder to a hard boride to a depth of approximately .001”, creating a “case-hardened carbide,” wherein a binder such as cobalt is converted at the surface to hard cobalt boride resulting in improved wear behavior. The soft metallic cobalt below the diffusion zone is retained providing optimum bulk properties, such as impact resistance. The conversion of cobalt to cobalt boride can result in significant improvements in properties such as erosion resistance, which is often limited by the continuous and relatively soft metal binder. Fig. 5 shows an improvement of 15 times in erosion resistance for a 6% Co-WC subjected to fine particle erosion at a 90° impingment angle.

Fig.5

A number of additional materials including cobalt-based alloys such as stellite, and many of the refractory metals can be Borofuse Processed. Molybdenum forms a particularly high hardness boride of approximately 3000 KHN.

Table 1

AiSI 3135 Pins AISI 1137 Blocks

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