Question

Vickers hardness uses

• A. Tungsten ball
• B. Steel ball
• C. Diamond pyramid
• D. Diamond cone

Hint:

Remember the characteristic indenter geometries for rapid elimination:
- Vickers \(\rightarrow\) Diamond Pyramid (136\(^{\circ}\) face angle)
- Rockwell C \(\rightarrow\) Brale Diamond Cone (120\(^{\circ}\) cone angle)
- Brinell \(\rightarrow\) Steel/Tungsten Carbide Ball
- Knoop \(\rightarrow\) Elongated Diamond Pyramid

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question asks about the specific indenter geometry and material utilized in the Vickers hardness testing method.
Hardness testing is a critical mechanical characterization technique used to determine a material's resistance to plastic deformation.
Each hardness testing standard is defined by a unique combination of indenter shape, material, and applied load.

Step 2: Key Formula or Approach:
The Vickers hardness test operates on the principle of microindentation.
The key formula to calculate the Vickers Hardness (HV) is:
\[ \text{HV} = \frac{2P \sin(\theta/2)}{d^2} \approx 1.8544 \frac{P}{d^2} \]
where:
\( P \) is the applied force in kgf.
\( \theta \) is the face angle of the diamond pyramid, which is precisely \( 136^{\circ} \).
\( d \) is the mean diagonal length of the indentation in mm.

Step 3: Detailed Explanation:

• Indenter Specifications: The Vickers test utilizes a square-based pyramid-shaped diamond indenter.
The opposite faces of this diamond pyramid meet at an angle of \( 136^{\circ} \), ensuring consistent geometrical similarity regardless of the depth of penetration.

• Comparison with Other Indenters:
- Brinell hardness testing utilizes a spherical hardened steel or tungsten carbide ball of standard diameters.
- Rockwell hardness testing employs either a spheroconical diamond cone (typically Brale indenter) or a steel ball indenter, depending on the scale (e.g., HRC or HRB).
- Knoop hardness testing uses an elongated, asymmetrical rhombic-based pyramid diamond indenter, which is suited for brittle materials or thin coatings.

• Process Advantages: Because the diamond indenter is incredibly hard and geometrically precise, it can test a wide range of materials from extremely soft to extremely hard.
The measurement is independent of the test force, which can vary from micro-loads of 1 gf to macro-loads up to 120 kgf.


Step 4: Final Answer:
Based on the standard definitions of metallurgical testing, the Vickers hardness test uses a diamond pyramid indenter.
Therefore, option (C) is the correct choice.