Synthesis of Cubic Boron Nitride Thin Films and Their
Application in Tool Inserts
A Thesis proposal
Submitted in partial fulfillment of the degree of
Master of Science
By
Prasanna Vemuri
TO
Graduate Committee
Dr. Seifollah Nasrazadani, Major Advisor
Dr. Reza Mirshams, committee Member
Dr. Philip Foster, Committee Member
Dr. Bruce Gnade, Committee member
Dr.Ping C. Sui, Industrial Representative
Department of Engineering Technology
College of Arts and Sciences
University of North Texas
10/10/2002
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Table of Contents
Introduction .................................................................................................................. 3
Problem Statement .................................................................................................... 4
Purpose of Research ................................................................................................. 5
Research Questions .................................................................................................. 6
Statement of Need ..................................................................................................... 6
Research Method ....................................................................................................... 7
Limitations .................................................................................................................... 7
Review of Literature ................................................................................................ 8
Methodology ................................................................................................................ 9
Summary ...................................................................................................................... 11
Thesis Timeline ........................................................................................................ 11
References ................................................................................................................... 12
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Introduction
Cubic boron nitride (cBN) is an attractive material for electronic and mechanical
applications under extreme circumstances because of its large band gap energy, high
room temperature thermal conductivity, high chemical inertness, good transmittance over
a large spectral range, and exceptional strength [1]. Because of these highly desirable
properties there has been an extensive worldwide effort to synthesize thin films of cBN.
Boron nitride, like carbon, has two main phases: hexagonal boron nitride (hBN), a
graphite-like material of low hardness, and cubic boron nitride which has the zinc blende
or diamond structure and is second only to diamond in hardness. It has the advantage
over diamond of low solubility in iron enabling it to be used for the machining of ferrous
materials. It is transparent to light over a wide wavelength range making it suitable for
wear resistant optical coatings. c-BN is capable of accepting both p-type and n-type
dopants giving it possibilities as a wide band gap semiconductor [2,3].
The cubic phase of boron nitride has significant technological potential for thin film
applications. Due to its high Vickers hardness of about 5000 kg/mm2 it is highly suitable
for hard, protective coatings. The fact that cBN does not react readily with ferrous metals,
can be deposited in thin film form at low temperatures and has a high resistance to
oxidation makes it even more attractive for tooling applications [4-6].
Recently, new processes for the deposition of cubic boron nitride have been investigated,
wherein BN films have been deposited from the vapor phase at low temperatures [7-10].
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There are many methods for preparing the c-BN thin films that can be classified mainly
into two areas: the Chemical Vapor Deposition (CVD) method and physical vapor
deposition (PVD) methods. Ion beam enhanced deposition (IBED) is one kind of the
PVD methods and in this process the growing thin film is bombarded by energized ions
[15].
Trends in the metal cutting industry are driven by the manufacturers need to continually
improve performance and reduce costs. The fundamental material characteristics that
enable cBN to enhance metal cutting operation are its extreme hardness, good toughness,
chemical inertness and high thermal conductivity. Today there is a significantly greater
and wider use of cBN tooling such as ball-nosed type cutters for the machining of dies
and moulds, machining of hard, medium hard and cast iron moulds [16].
Problem Statement
Cubic boron nitride thin films are to be deposited on a Si (100) substrate and a Tungsten
Substrate by using Electron beam evaporator and their properties are to be characterized.
Application of cBN as cutting tool inserts is to be presented.
Other processes for the preparation of cBN have been reported, such as activated reactive
evaporation with a gas activation nozzle [11], reactive rf sputtering [12], ionized
evaporation [13], plasma chemical transport [14], rf plasma chemical vapor deposition
[15]. However, the obtained films consisted of cBN and hBN or amorphous BN, and the
content of cBN was not high.
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The Characterization of the cubic boron nitride thin film include both chemical and
mechanical characterizations. In chemical characterization, Raman Spectroscopy, FTIR,
Scanning Electron Microscopy, X- Ray Diffraction, Transmission Electron microscopic
analysis can be performed. Mechanical characterization includes measurement of residual
stresses using XRD.
The films deposited with solid boron and nitrogen gas are to be characterized by x ray
diffraction and transmission electron microscopy to determine the composition of the
film. FTIR absorption spectra of the films show absorption bands at particular
wavelengths indicating the formation of a cBN.
Purpose of Research
The purpose of this research is to enhance the scope of cubic boron nitride in variegated
fields and establish its importance among other related materials. The main stress in this
study is to:

Synthesize the cBN thin films using Electron Beam Evaporator

Characterize the CBN films using different characterization procedures such as
SEM, XRD, FTIR etc.,

Determine the application of cubic boron nitride films as cutting tool inserts.
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Research Questions
This thesis will attempt to provide detailed knowledge of synthesis of cBN using
Electron Beam Evaporator and their application in tooling industry as cutting tool
inserts.
 In what way cubic boron nitride films produced from Electron beam evaporation
more capable than the ones produced from other processes?
 How the data developed from this research help to decide which form of boron
nitride is best useful?
 What significant capabilities can be accomplished if cubic boron nitride films are
used in tooling industry?
The answer, (the explication and defense of which will form the substance of this
thesis), is a frame work of comparison tables and visualization methods (charts, graphs
etc.,) that can be developed allowing to quantitatively analyze and apply cubic boron
nitride films in the tooling industry. This thesis will present, demonstrate and compare
available cutting tool inserts being used in tooling industry, thus allowing to select the
most appropriate material for a particular application.
Statement of Need
Due to their excellent physical and chemical properties such as very high hardness,
high resistance to wear, high thermal and chemical stability, cBN has prominent
applications in coating for cutting tools, optics and electronic devices. It is second
hardest material known next to diamond and has many attributes such as excellent
chemical inertness, especially against ferrous metals unlike diamond [4].
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Existing approaches for the preparation of cBN such as reactive rf sputtering, ionized
evaporation, ion beam evaporation etc are not very efficient as the obtained films
consisted of very less amount of the cBN. These issues stress the need for effective
method for the synthesis of cBN thin film. The data from this research should enable to
review the method that could produce considerable amount of cBN with right
combination of properties.
Research Method
The research method for this study is experimental. Cubic boron nitride thin films are
produced using electron beam evaporation and the films obtained are deliberately tested
using FTIR, SEM, XRD etc., to determine the percentage growth of cBN and their
ability to be applied as cutting tool inserts. The results will be analyzed and rationalized
using existing methodologies and techniques. A detailed explanation of the
methodology and procedures selected for this study are presented in later sections of
this proposal.
Limitations
One of the main limitations in this research will be inability to deposit in large-scale
cBN thin films. This research discusses only limited applications of cBN thin films.
Huge level of intrinsic stress can be possibly induced. This will not provide a detailed
description of all the properties of cBN thin films.
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Review of Literature
From review of literature it is found that the current methods used for the deposition of
cBN thin films are not very efficient as the films obtained from those processes contained
very small amount of cubic boron nitride [1-3]. Some recent efforts attempt to deposit
considerable amount of cBN thin films, which will be cost effective and at the same time
can be very efficiently used for hard coatings. Boron nitride exists in two main
crystalline forms namely hexagonal boron nitride and cubic boron nitride, which are
structurally similar to graphite and diamond respectively. Cubic boron nitride exhibits
excellent physical and chemical properties and can be used in several applications such as
protective coatings for cutting tools and semiconductor layers in electronic devices, due
to its chemical inertness and stability at high temperature [4]. Various ion-assisted
physical and chemical vapor deposition techniques have been successfully used to
produce cBN films, in which an adequate ion impact is considered to be indispensable for
the formation of the cubic phase [15]. However, the ion bombardment during deposition
also builds up extremely high compressive stresses, and consequently leads to poor
adhesion of the resulting coatings [17-20]. Therefore, stress reduction and adhesion
improvement have become a challenging task in recent investigations. Several studies
such as post-deposition ion implantation, buffer layers etc., have been performed, but
with limited success. [21-24].
Under optimized conditions, most of the cBN thin films prepared were found to be a
three-layered structure, an initial amorphous boron nitride layer on a substrate, followed
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by a highly oriented turbostratic boron nitride layer with its c-axis parallel to the substrate
surface, and a final cBN layer. Due to the existence of the initial sp2- bonded boron
nitride transition layer and some turbostratic boron nitride mixed in the cBN layer, the
purity of cBN films is low, making them less efficient. In particular, cBN films prepared
by CVD techniques were reported to have lower cubic phase content than those prepared
by PVD techniques because of the relatively thick initial layer [25].
Methodology
As a diamond like material, cubic boron nitride exhibits many extreme properties. After
diamond, cBN is the second hardest material known. It is superior to diamond as a wear
resistant coating mainly because of its chemical inertness at high temperatures towards
iron, cobalt, nickel and oxygen. In this research, deposition of cubic boron nitride using
electron beam evaporator will first be discussed, and then the films produced will be
characterized using different techniques such as SEM, TEM, XRD, FTIR etc., followed
by the residual stress analysis of the film produced. Finally the scope of cBN in the
tooling industry will be discussed. First part of this research will discuss method of
producing cBN and then determine their properties. Later part will consider the
characterization of cBN and discuss their capabilities and applications in different fields.
It also deals with how cBN can be best utilized as cutting tool inserts. A detailed analysis
of the multi-level approach methodology is as follows:
First step: Production of cubic boron nitride: A variety of chemical vapor deposition and
physical vapor deposition techniques can be used to prepare cBN thin films. In the CVD
process three-layered structure of cBN films prepared were found an initial amorphous
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boron nitride layer on a substrate, followed by a sp2 bonded BN transition layer and a
final cBN layer. Due to the presence of this transition layer the purity of cBN films will
be low. Therefore films prepared by CVD techniques have lower cubic phase content
than those prepared by PVD techniques because of the relatively thick initial layer. In this
research cBN will be produced using the electron beam evaporator, which is a PVD
technique. The formation of cBN with high fraction of the cubic phase is only possible
with specific values of process parameters. These parameters are to be determined to
obtain better films of cBN.
Second step: Characterizing the cBN thin films: Growth of cBN film will be studied
using a FTIR. The FTIR absorption spectra of the films show the absorption bands
indicating the formation of a cBN phase.
To investigate the crystal structure X-Ray Diffraction can be employed and the
composition of the film can be determined using a transmission electron microscope or a
scanning electron microscope.
The hardness of the cBN thin film produced can be measured using a nanoindenter from
which the young’s modulus of the film can also be determined.
The later part of this section will deal with the analysis of the film based on the results
obtained from the characterization.
Third Step: Application of cBN as a cutting tool insert: In this step the capabilities and
applications of cBN thin films will be discussed. Due to its extreme hardness cBN film
will be investigated for their application as cutting tool inserts.
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Summary
The focus of this study will be on deposition of cBN thin film, an analysis of the film
obtained and discussion of their applications in tooling industry. The summary will
include:

Answers to the Research Questions

Conclusions based on results and analysis of the study

Alternative explanations for the findings

Strengths of the study

Weakness of the study
Thesis Timeline
This research started in May 2002 and will be completed during May 2003 semester. The
introduction chapter, the review of literature, and methodology chapter should be
completed by the end of September. Data collection and the results and analysis chapter
should be completed by the end of February. The summary chapter should be completed
by the middle of May. A detailed time line will be framed if the study is approved.
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References
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Materials Science Forum, Vols.54 and 55, Trans Tech Publ., Aedermannsdorf, 1990.
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