Dispersion strengthening

It's the mechanism of strengthening in metals by adding dispersed second phase material.

1. PRESENTATION ON DISPERSION STRENGHTHENING OF COMPOSITES By : Sanjeev Kumar Verma M. Tech. 1 st year (12307EN045) Department of Metallurgical Engg. IIT (BHU),Varanasi 4/10/2013

2. CONTENT Introduction Classification of composites materials Definition of dispersion strengthening Mechanism Influence of the strengthening Precipitation Vs dispersion strengthening Summary References 1 4/10/2013

3. Introduction: The strength and hardness in some metal alloys may be enhanced by the presence of extremely small and uniformly dispersed particles within the original phase matrix. Whether introduced as insoluble particles in powder compaction (dispersion strengthening). Second phase particles are generally the most potent strengthening agent in practical high strength engineering materials. The size, shape, and amount of second phase particles controls the mechanical properties of the alloy. 2 4/10/2013

4. Classification of composites Composites Particle-reinforced Fiber-reinforced Structural Large particle Dispersion strengthened Continuous (aligned) Discontinuous (short) laminates Sandwich Randomly oriented Aligned 3 4/10/2013

5. The process which produces dislocation pining sites due to the presence of second phase particles in the matrix of the first phase. Normally Hard particles size rang . 1nm up to 1μm Dispersion Strengthening Ductile Matrix Hard particles Powder metallurgy Composite materials Examples: 14%Al2O3 in Al- “SAP” Composite 1-2%ThO2 in Ni-20%Cr-TD nickel WC in CO- Cemented Carbide cutting tools fig: 1 Powder metallurgy processes 4 4/10/2013

6. Mechanism Orownan Model The shear stress required to bow a two particles separated by Straight dislocation line approaching two particles. Initially line to bend. Reached to critical curvature. Leaving a dislocation loop around each particle. fig: 2 Stages in passage of a dislocation Dislocation Bypass by the Orowan Bowing Mechanism: 5 4/10/2013

7. Factors influencing second-phase particle strengthening Interparticle spacing Average particle diameter Strength Volume fraction Ductility Distribution (interspacing distance) If the contributions of each phase are independent, the properties of the multiple phase alloy is the summation of a weighted average of individual phases. For example: 6 Where V= volume fraction V=V1+V2+----Vn 4/10/2013

8. Strengthening Particle Radius f – volume fraction of particles r – particle radius Strengthening effect can be estimated as : G – Shear Modulus r – Particle radius b – Burgers vector f – volume fraction of particles - strain field factor Strengthening Particle Radius Curve f or big particles Curve for small particles Dispersion Hardening big and Small particles 7 4/10/2013

9. Difference between precipitation and Dispersion Strengthening Coherency occur in PS but No coherency presence in DS. DS stable at all temperatures but PS is not stables. Time factor not important for DS but PS time factor important. Any alloy can be made in case DS. In DS chemical stability is increase than PS. PS-isotropic and DS- Anisotropic fig:3 Coherency PS fig:4 No coherency DS 8 4/10/2013

10. Advantage And Disadvantages Advantages: Higher creep resistance Higher temperature sustain Automotives industries Aerospace areas Sporting goods industries Disadvantages: Not use for only higher strength purpose. Uniform distribution of the particles 9 4/10/2013

11. Summary of dispersion strengthening Very favorable for high-temperature strengthening since dispersoids can not dissolve. Due to incoherency particle cutting can not occur. Main problem: distribute fine particles homogeneously and at high particle number density. 10 4/10/2013

12. References 11 George E.Dieter,Mechanical Metallurgy SI Metric Edition, McGraw-Hill Science in Materials and Engineering, William D.Callister , Jr.Materials Science and Engineering-In Introduction six ediation,Joh Wiley& Sons’2007 Luker Fischer, “Nano-Dispersion Particulate Strengthened Metal Matrix Composites”,2004,P4-10 4/10/2013

13. THANK YOU 12 4/10/2013