Dispersion strengthening

Dispersion strengthening

• 1.
  PRESENTATION ON DISPERSION STRENGHTHENING OF COMPOSITES By: Sanjeev Kumar Verma M. Tech. 1st year (12307EN045) Department of Metallurgical Engg. IIT (BHU),Varanasi 4/12/2013
• 2.
  CONTENT • Introduction •Classification ofcomposites materials • Definition of dispersion strengthening • Mechanism • Influence of the strengthening • Precipitation Vs dispersion strengthening • Summary • References 4/12/2013 1
• 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 4/12/2013
• 4.
  Classification of composites Composites Particle-reinforced Fiber-reinforced Structural Large Dispersion laminates Sandwich particle strengthened Continuous Discontinuous (aligned) (short) Randomly Aligned oriented 4/12/2013 3
• 5.
  Dispersion Strengthening 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 Hard Composite Ductile Powder particles materials Matrix metallurgy 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 4/12/2013 4
• 6.
  Mechanism Orownan Model Dislocation Bypass by the Orowan Bowing Mechanism:  The shear stress required to bow a two particles separated by   ~ Gb /  fig: 2 Stages in passage of a dislocation  Straight dislocation line approaching two particles.  Initially line to bend.  Reached to critical curvature.  Leaving a dislocation loop around each particle. 5 4/12/2013
• 7.
  Factors influencing second-phaseparticle strengthening  Interparticle spacing    Average particle diameterD  Strength  Volume fraction V f  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:  avgV 1 1V 2 2       V n n Where V= volume fraction  avgV 1 1V 2 2     V n n V=V1+V2+----Vn 4/12/2013 6
• 8.
  Dispersion Hardening bigand Small particles Strengthening Strengthening effect can be estimated as: r   6G ( ) 0.5 f 0.5 1.5 b G – Shear Modulus r – Particle radius Particle Radius b – Burgers vector Curve for small particles f – volume fraction of particles  - strain field factor 4(1  f )r  Strengthening 3f f – volume fraction of particles r – particle radius Particle Radius Curve for big particles 4/12/2013 7
• 9.
  Difference between precipitationand Dispersion Strengthening Coherency occur in PS but No coherency presence in DS. DS stable at all temperatures but PS is not stables. fig:3 Coherency PS fig:4 No coherency DS 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 4/12/2013 8
• 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 4/12/2013 9
• 11.
  Summary of dispersionstrengthening  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. 4/12/2013 10
• 12.
  References  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 4/12/2013 11
• 13.
  4/12/2013 12