13 CHAPTER 2 LITERATURE SURVEY 2.1 INTRODUCTION The objectives of the present study calls for a closer review of the following topics: Biomaterials Surface engineering AISI 316L Stainless Steel Ion implantation Quench Polish Quench process Corrosion studies Hardness studies Wear studies Design of Experiments Genetic Algorithms A literature review was carried out to understand and assess the current status of the above areas. This chapter is organized in the order mentioned above.
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CHAPTER 2
LITERATURE SURVEY
2.1 INTRODUCTION
The objectives of the present study calls for a closer review of the
following topics:
Biomaterials
Surface engineering
AISI 316L Stainless Steel
Ion implantation
Quench Polish Quench process
Corrosion studies
Hardness studies
Wear studies
Design of Experiments
Genetic Algorithms
A literature review was carried out to understand and assess the
current status of the above areas. This chapter is organized in the order
mentioned above.
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2.2 BIOMATERIALS
William (1964) defines biomaterials as “nonviable materials used
in medical devices, intended to interact with the biological systems”. Sujata
V. Bhat (2002) stated that the Romans, Chinese, and Aztecs used gold in
dentistry over 2000 years ago.
Hench and Ethridge (1982) discussed the usefulness of biomaterials
in replacing a part or a function of a body in a safe, reliable, economic and
physiologically acceptable manner. There are several types of biomaterials
used in orthopedics, density, neurological and etc. Jagielski et al (2006)
discussed the uses of biomaterials in detail. Biomaterials are used for making
devices that can interact with biological systems to coexist for longer service
with minimum failure. Materials used for transplantation have to fulfill very
strict requirements, the most important being those imposed by biological
reasons like blood and tissue compatibility and mainly, the mechanical
properties.
Artificial materials used for implants in medicine and dentistry,
traditionally employ titanium and its alloys, as well as stainless steel because
of its high fracture and corrosion resistance, easy handling and cost
effectiveness. Surface modification of biomaterials is being widely practised
to improve their performance since biomaterials are intended to expose to a
variety of aggressive body liquids. Pramatarova et al (2007) have dealt with
this problem in detail.
Chu et al (2002) discussed the importance of designing biomaterials
with the best surface properties to be used for implants. These properties must
possess along with the desired bulk properties that meet other requirements,
especially mechanical properties in order to function properly in a bio-
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environment. To enhance the surface properties it would be desirable to arrive
at adequate bulk properties followed by a special surface treatment. In this
way, it allows one to make ideal biomaterials with surface attributes that are
decoupled from the bulk properties. Further, the surface properties can be
selectively modified to enhance the performance of the biomaterials. Jagielski
et al (2006) dealt with the surface treatments of biomaterials. Advanced
biological materials require an appropriate surface treatment ensuring the best
possible interface between implant and human body and optimum functional
properties. Pramatarova et al (2007) indicated that the material surfaces play a
critical role in biology and medicine since most biological reactions occur on
surfaces and interfaces. Xuanyong Liua et al (2004) have dealt with the
surface characterization. The surface characterization of biomaterials is
particularly important when biomaterials are going to be designed. This is not
an easy task considering different surface properties that are most likely to
play an important role in the reaction of the host’s body to the artificial
material.
2.3 SURFACE ENGINEERING
Since most of the reactions occur on surfaces and interfaces,
Pramatarova et al (2007) studied the role of material surfaces in biology and
medicine. There are many examples to demonstrate the fact that the surface
properties of the materials control and are directly involved in biological
reactions and processes. Cui and Luo (1999) insisted on the importance of
surface-engineered biomaterials. The importance of surface-engineered
biomaterials to the longevity of medical implants has been recognized by both
major medical device companies and by more and more patients. In bone
replacement, especially long bone and joint replacements, metal implants are
widely used to take the unsubstituted position. Although the metallic
orthopedic implants might have excellent bulk properties such as ideal
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strength and elasticity, it has relatively poor surface properties, e.g. poor wear
resistance and limited biocompatibility. It is therefore necessary to make a
compromise between bulk and surface properties. Bharat Bhushan (1999)
showed the commonly used coating deposition techniques and surface
treatments.
2.4 AISI 316L STAINLESS STEEL
Zbeka et al (2002) discussed the selection of the material type for
biomedical applications. Metals are the most favored materials in orthopedic
surgery and particularly in total hip replacement, because of their good
mechanical stability. On the other hand, metals corrode in contact with
aggressive body fluids or tissue. Therefore, the designer must be careful while
selecting materials of this type.
Tomonori Nakanishi et al (2007) have dealt with the metallic
materials for biomedical application. Metal materials are chosen as
osteosynthesis implants for internal fixation in fractures nowadays: in
particular, austenitic stainless steel (e.g. AISI 304, AISI 316L) has been
widely used for many cases because of the following qualities: Excellent
mechanical properties, corrosion resistance, sufficient formability, and cost
effectiveness. However there are many problems related to plate breakage and
irritation with respect to the fixation devices for osteosynthesis treatment.
Gurappa (2002) dealt with the problems in metallic materials. Although the
metallic orthopedic implants might have excellent bulk properties such as
ideal strength and elasticity, it has relatively poor surface properties, e.g. poor
wear resistance. It has been reported that stainless steel corrodes in vivo. Cui
and Luo (1999) explored the problems related to wear. In case of hip
replacement, the wear debris from the implant is one of the important factor
for the aseptic loosening, which is a frequent cause of failure of the prosthetic
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implants. It is generally accepted that improving the wear resistance and
biocompatibility by surface engineering is an optimal option.
Liu Chenglong et al (2005) found some of the applications of AISI
316L stainless steel to be useful in biomedical implants, such as orthopedic,
cardiovascular and dental devices. Metin Usta et al (2004) did considerable
research on the use of 316L austenitic stainless steel for implant fabrication
because of its greater resistance to corrosion than carbon and low-alloy steel,
primarily due to the presence of chromium. Surface modification methods are
widely used in order to improve corrosion resistance, wear resistance, and
fatigue strength of 316L stainless steel.
The properties of AISI 316L have been dealt with in detail by
Zbeka et al (2002). Austenitic stainless steel, as their name implies, has an
austenitic microstructure at room temperature and cannot be hardened to any
great extent by heat treatment, although it can be appreciably strengthened by
cold work. Gurappa (2002) studied the applications of AISI 316L SS in
reconstructive surgery, heart valve parts, wire leads, aneurysm clips and
dental uses. He further stated that AIS1 316L stainless steel is the most widely
used stainless steel for medical and dental applications. Metin Usta et al
(2004) studied the applicability of 316L SS in situations where corrosion
resistance is required and found out that the inclusion of molybdenum
enhances resistance to pitting corrosion in salt water.
Liu Chenglong et al (2005) have dealt with the corrosion of
implants inside the body and listed the applications of AISI 316L SS. In
recent years, the application of protective coatings for implants has been
attracting considerable attention. TiN film is an interesting choice for
implants due to some of its useful properties, such as chemical stability, high
hardness, excellent wear properties, electrical properties and intrinsic
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biocompatibility. Zhu and Lei (2005) concluded that the austenitic stainless
steel and its alloys are successfully used in surgical implants, because of their
ease of fabrication and reasonable resistance to corrosion. Pramatarova et al
(2007) studied the use of titanium and stainless steel in medicine and dentistry
because of its high fracture and corrosion resistance, easy handling and
comparatively low cost.
2.5 SURFACE MODIFICATION TECHNIQUES
Various surface modification techniques have been applied to
improve the properties of AISI 316L SS. Some of these studies are
summarized below: De Oliveira et al (2003) studied the effect of the
temperature of plasma nitriding on AISI 316L austenitic stainless steel.
Double layers of nickel and aluminum were electroplated on 316L stainless
steel by Kannan et al (2005). Fossati et al (2006) studied the properties of