Co-based Alloys and Their Applications
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Questions and Answers

Which Co-based alloy is primarily used for casting products?

  • CoNiCrMoWFe alloy
  • CoCrMo alloy (correct)
  • CoCrWNi alloy
  • CoNiCrMo alloy

    • Co-based alloys can contain up to 35% chromium.

    False

    Name one application of the wrought CoNiCrMo alloy.

    Stems of prostheses for heavily loaded joints.

    The two basic elements of Co-based alloys are cobalt and ______.

    <p>chromium</p> Signup and view all the answers

    Match the following Co-based alloys with their respective types:

    <p>F75 = Cast CoCrMo alloy F90 = Wrought CoCrWNi alloy F562 = Wrought CoNiCrMo alloy F563 = Wrought CoNiCrMoWFe alloy</p> Signup and view all the answers

    What is added to Co-based alloys to produce finer grains?

    <p>Molybdenum</p> Signup and view all the answers

    There are four types of Co-based alloys according to ASTM recommended for surgical implants.

    <p>True</p> Signup and view all the answers

    What process is used to create castable CoCrMo alloy?

    <p>Melting and pouring into a mold.</p> Signup and view all the answers

    What is the primary function of carbon in steel?

    <p>Increase strength</p> Signup and view all the answers

    Vanadium helps develop a coarser crystalline microstructure in steel.

    <p>False</p> Signup and view all the answers

    What percentage range of carbon is typically found in structural steels?

    <p>0.15 to 0.30 percent</p> Signup and view all the answers

    Nickel enhances the __________ behavior of steel at low temperatures.

    <p>fracture toughness</p> Signup and view all the answers

    Match the following elements with their effects on steel:

    <p>Carbon = Increases strength, reduces ductility Nickel = Enhances corrosion resistance and fracture toughness Vanadium = Develops finer crystalline microstructure Manganese = Improves hardenability</p> Signup and view all the answers

    Which of the following metals is NOT commonly used for manufacturing implants?

    <p>Platinum (Pt)</p> Signup and view all the answers

    All metals used in implants are biocompatible and do not corrode in the body.

    <p>False</p> Signup and view all the answers

    What is the effect of too much carbon in steel?

    <p>Too low ductility</p> Signup and view all the answers

    The nickel content in certain grades of ASTM A514 can go up to 1.50 percent.

    <p>True</p> Signup and view all the answers

    What are metals containing two or more elements called?

    <p>Alloys</p> Signup and view all the answers

    The ability of a material to perform within an appropriate host response in a specific application is known as __________.

    <p>biocompatibility</p> Signup and view all the answers

    What is the typical vanadium content in ASTM grades A572 and A588?

    <p>0.02 to 0.15 percent</p> Signup and view all the answers

    Match the following elements with their significance in the body:

    <p>Fe = Essential for cell functions Co = Synthesis of vitamin B12 Cu = Crosslinking of elastin in the aorta Ti = Commonly used in implants</p> Signup and view all the answers

    What is a potential consequence of corrosion in metallic implants?

    <p>Weakened implant structure</p> Signup and view all the answers

    Cytotoxic substances are harmless to cells.

    <p>False</p> Signup and view all the answers

    What type of alloys are commonly used in the context of biomedical implants?

    <p>Co-based alloys and Ti-based alloys</p> Signup and view all the answers

    What is the typical amount of molybdenum in certain grades of A588 steel?

    <p>0.08 to 0.25 percent</p> Signup and view all the answers

    Chromium primarily increases the strength of steel.

    <p>False</p> Signup and view all the answers

    What is the composition of the well-known '18-8' stainless steel?

    <p>18% nickel and 8% chromium</p> Signup and view all the answers

    The first stainless steel developed was type ______.

    <p>302</p> Signup and view all the answers

    What is the primary benefit of adding molybdenum to steel?

    <p>Improves strength at high temperatures</p> Signup and view all the answers

    Match the following stainless steel types with their specific compositions:

    <p>18-8 = 18% nickel and 8% chromium 18-8Mo = 18% nickel, 8% chromium, and molybdenum 316 = 16% nickel, 10% chromium 316L = 16% nickel, 10% chromium, and lower carbon</p> Signup and view all the answers

    Stainless steel types containing molybdenum are more resistant to corrosion than other stainless steels.

    <p>True</p> Signup and view all the answers

    Stainless steel type ______ is known for its improved resistance to chloride solution due to lower carbon content.

    <p>316L</p> Signup and view all the answers

    What are the main alloying elements in the titanium alloy Ti6Al4V?

    <p>Aluminum and Vanadium</p> Signup and view all the answers

    Titanium has a high shear strength, making it desirable for bone screws and plates.

    <p>False</p> Signup and view all the answers

    What type of oxide forms on titanium that contributes to its corrosion resistance?

    <p>Titanium dioxide (TiO2)</p> Signup and view all the answers

    The alloy Ti6Al4V contains _____% aluminum.

    <p>5.5–6.5</p> Signup and view all the answers

    Match the following properties to their descriptions:

    <p>Strength = Similar to 316 stainless steel Oxidation Resistance = High due to aluminum content Shear Strength = Poor Corrosion Resistance = Achieved via oxide layer formation</p> Signup and view all the answers

    What is the primary reason for titanium's corrosion resistance?

    <p>Formation of a solid oxide layer</p> Signup and view all the answers

    Higher impurity content in titanium alloys leads to lower strength.

    <p>False</p> Signup and view all the answers

    What phenomenon demonstrates how corrosion is inhibited in metals?

    <p>Passivity</p> Signup and view all the answers

    What is the composition of the CoNiCrMo alloy originally called MP35N?

    <p>35% Co and 35% Ni</p> Signup and view all the answers

    Titanium has a higher density than wrought CoNiCrMo alloys.

    <p>False</p> Signup and view all the answers

    What elements' impurity contents must be controlled in titanium for implant applications?

    <p>Oxygen, iron, and nitrogen</p> Signup and view all the answers

    The titanium density is ____ g/cm³.

    <p>4.5</p> Signup and view all the answers

    Match the following titanium compositions with their correct max percentages:

    <p>Oxygen = 0.40% Iron = 0.50% Carbon = 0.08% Nitrogen = 0.05%</p> Signup and view all the answers

    What effect does reducing carbon content have on wrought cobalt-chromium alloys?

    <p>Reduces strengthening</p> Signup and view all the answers

    Adding nickel generally increases chromium content in cobalt-chromium alloys.

    <p>False</p> Signup and view all the answers

    In which decade did the attempts to use titanium for implant fabrication begin?

    <p>1930s</p> Signup and view all the answers

    Study Notes

    Metallic Materials

    • Metallic biomaterials are primarily used for load-bearing applications, such as knee or hip implants, dental implants, and fracture fixations.
    • Alloys, consisting of two or more elements, are more common than pure metals, offering greater corrosion resistance and/or strength.
    • Pure metals, like copper, gold, silver, and platinum, are occasionally found in nature in their metallic state.
    • Other metals, like aluminium, are mostly found in minerals (e.g., bauxite).
    • The strength of pure metals is affected by dislocations occurring at grain boundaries.
    • Alloys' strength is enhanced by preventing physical dislocations of their lattice structure due to varying sizes of metal elements.
    • Metals used in implants ( iron, chromium, cobalt, nickel, titanium, tantalum, molybdenum, and tungsten) are generally tolerated by the body in small quantities.
    • Some naturally occurring metals are essential for bodily functions, but excessive amounts can be harmful.
    • Biocompatibility is critical for implant metals. Corrosion can weaken the implant and release potentially harmful corrosion products into tissues.
    • Biocompatibility refers to a material's ability to perform an appropriate host response within a specific use.

    Outline of Metallic Materials

    • Stainless steels (alloys of nickel, iron, chromium, manganese).
    • Cobalt-based alloys (combination of cobalt, chromium, molybdenum, and sometimes other elements).
    • Titanium and titanium-based alloys.
    • Corrosion of Metallic Implants.

    Compositions of Steel

    • Important chemical element in structural steel is Carbon (C).
    • Increasing the carbon content in steels increases strength but decreases ductility.
    • Structural steels contain carbon between 0.15 and 0.30 percent.
    • Nickel (Ni) improves corrosion resistance and low-temperature fracture toughness.
    • Vanadium (V) contributes to a finer crystalline microstructure and increased fracture toughness.
    • Molybdenum (Mo) enhances strength at higher temperatures and corrosion resistance, typically used in amounts of 0.08-0.25% in A588 steel, and 0.15-0.65% in different types of A514.
    • Chromium (Cr) primarily increases corrosion resistance, frequently found with nickel and copper in stainless steel.
    • Different types of stainless steel include 18-8 (type 302) and 18-8Mo (type 316), varying in carbon content and resistance to specific environments (saltwater).

    Types and Composition of Stainless Steels

    • Chromium is crucial for stainless steel's corrosion resistance, requiring a minimum of 11%.
    • Classification of stainless steels includes austenitic, martensitic, ferritic, duplex, and precipitation-hardenable (PH).

    Austenitic Stainless Steel

    • Microstructure is attributable to the addition of nickel, manganese, and nitrogen.
    • These steels have excellent weldability and formability.
    • Corrosion resistance can be enhanced by the addition of chromium, molybdenum, and nitrogen.
    • Generally non-magnetic.
    • Applications include medical devices demanding good corrosion resistance and moderate strength (canulae, dental tools, needles).

    Martensitic Stainless Steel

    • These steels have a similar structure to ferritic steels but contain more carbon (up to 1%).
    • Hardening and tempering are possible characteristics.
    • Primarily used in applications requiring high strength and moderate corrosion resistance (for example, machine parts).

    Co-Based Alloys

    • Commonly referred to as cobalt-chromium alloys.

    • Two main categories: cast (CoCrMo) and wrought (CoNiCrMo)

    • Cast alloys are often used for casting products or artificial joints.

    • Wrought alloys are used for the stems of heavy-duty joints (like knee and hip).

    • ASTM lists four common Co-based alloy types for surgical implants

    Ti and Ti-Based Alloys

    • Titanium was initially used in implants in the late 1930s.
    • Titanium is lightweight compared to stainless steel or cobalt-based alloys.
    • Titanium's good biocompatibility allows for tolerance in applications.
    • Four grades of unalloyed titanium are often used in implants.
    • Oxygen, iron, and nitrogen are crucial impurities, which affect ductility and strength.
    • Chemical composition varies depending on the intended use of the Ti alloy. A notable alloy is Ti6Al4V.

    Corrosion of Metallic Implants

    • Titanium's corrosion resistance stems from the formation of a stable oxide layer (TiO2).
    • The oxide layer passivates the titanium, preventing further corrosion.
    • Surface passivation (using acid solutions) is frequently applied to metal implants to create an oxide layer for corrosion resistance and to act as insulator.
    • Alloys are typically more resilient to corrosion after implantation due to the greater stability of the oxides that are created, compared to pure metals.

    Passivity

    • It's a phenomenon in which materials resist corrosion in a specific environment.
    • This phenomenon can be explained through an oxide film theory.
    • In the oxide film theory, an oxide layer forms from the exposure to environment, thus isolating the metal and slowing down any potential reactions.

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    Description

    Test your knowledge on the different types of Co-based alloys and their specific applications, particularly in casting and surgical implants. This quiz includes questions about alloy composition, manufacturing processes, and the effects of various elements on steel and cobalt-based alloys.

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