DIAMOND

Prepared by:

A. ShapiroTitanium Brazing, Incorporated

Contents

Introduction 624

Base Materials 624

Interaction ofDiamond withLiquid Metalsand Alloys 626

Brazing FillerMetals andBrazing Processes 628

Applications 634

Bibliography 635

SuggestedReading List 636

CHAPTER 36

Photograph courtesy of Dr. Manfred Boretius, Listemann AG

AWS BRAZING HANDBOOK 623

INTRODUCTION

624 CHAPTER 36—DIAMOND AWS BRAZING HANDBOOK

Diamond, the hardest material known, findsnumerous applications in industry, especially in themanufacture of ultrahard abrasives, metal machiningtools, and drilling tools for oil and gas wells. Despitetheir high cost, diamonds are very effective toolmaterials. For example, the tool life of a polycrystal-line sintered diamond is about 40 times longer thanthat of a traditional WC-Co cemented carbide cut-ting tool used for machining aluminum alloys. Otherwell-known applications include jewelry and elec-tronic devices—particularly the heat sinking of dia-mond films and laminates, which employs extremelyhigh thermal conductivity, another unique propertyof diamonds.

Brazing is the most reliable method of joining dia-mond to metals or ceramics. For this reason, manymanufacturing companies and researchers concen-trate their efforts on the research and development ofdiamond brazing technologies. This chapter reviewsthe conventional industrial materials and processesused to braze diamonds and presents promising newapproaches that will hopefully be realized in the nearfuture.

BASE MATERIALS

Five forms of diamond are available as ultrahardabrasive and cutting tool materials. They are asfollows:1

1. Natural single-crystal diamonds,2. Synthesized single-crystal diamonds,3. Polycrystalline diamonds (PCD) sintered at a

high temperature and pressure,

1. Prelas, M. A., G. Popovichi, and L. K. Bigelow, 1998, Hand-book of Industrial Diamonds and Diamond Films, New York:Marcel Dekker, pp. 1135–1144.

4. Thick-film chemical-vapor-deposited (CVD)polycrystalline diamonds up to 0.04 inch (in.)(1 mm), and

5. Thin-film chemical-vapor deposited (CVD)polycrystalline {0.002 in. [<50 micrometers(µm)]} diamonds.

The physical and mechanical properties of these dia-mond forms are compared in Table 36.1.

Thick-film CVD diamonds are manufactured inthe form of wafers up to 0.04 in. (1 mm) thickand about 6 in. (150 mm) in diameter. These arecut by laser beam and brazed onto cemented carbideor a silicon nitride sunstrate. Thin-film CVD filmsare nucleated and deposited for cutting tools ontosilicon nitride, silicon carbide, and WC-Co (witha low cobalt content, <6 wt %) cemented carbidesubstrates.2

Diamonds are also classified by the presence ofimpurities or secondary phases. Most natural crys-tals belong to Type 1a, characterized by 0.1% nitro-gen atoms in the form of small aggregates. Mostsynthetic diamonds are of Type 1b and contain dis-persed nitrogen. Diamond crystals of Type IIa aresubstantially free of nitrogen and have enhancedoptical and thermal properties. Very pure blue dia-monds of Type IIb exhibit semiconducting propertiesdue to a small content of boron.

Diamond possesses the highest hardness and high-est thermal conductivity of any material at roomtemperature. The thermal conductivity of diamondcrystals is as high as five times that of copper atroom temperature.3 The unique combination ofthese two properties renders it the ultimate cuttingand abrasive material. Diamond not only cuts thetreated substance but also rapidly dissipates the heat

2. Davis, R. J., ed., 1995, Ultrahard Materials, in Tool Materials,ASM Specialty Handbook,® Materials Park, Ohio: ASM Inter-national, pp. 85–100.3. See Reference 2.

DIAMONDCHAPTER 36