DESIGN OF COST- EFFECTIVE BULK METALLIC GLASS COMPOSITES

Transcription

1 DESIGN OF COST- EFFECTIVE BULK METALLIC GLASS COMPOSITES Laura M. Andersen ASM San Diego Chapter April 24, 2012 Advisor: Prof. Kenneth S. Vecchio Chair, Department of NanoEngineering Materials Science and Engineering Program University of California, San Diego

2 What are metallic glasses (amorphous metals)? Liquid metal cooled at a sufficiently high rate (10 6 K/sec) à Freeze random orientayon of atoms in the liquid state à Characterized by a non- crystalline atomic structure Nearly every metal can form an amorphous structure if cooled fast enough à Limits thickness: 10s or 100s of microns Figure: Inoue et al, Sci. and Tech. of Adv. Mats., 2000

3 Bulk metallic glasses (BMG) Amorphous structure with low cooling rates: Tightly bound clusters of atoms Maximum density on local scale Random long- range order Defined short to medium range order R c = K/sec D max = 1 30 mm OpYmize glass forming ability (GFA): ComposiYon control Atomic size mismatch Deep eutecycs

4 Why should we study metallic glasses? Unique properyes: High hardness, wear resistance Excellent corrosion resistance High strength/weight rayo Superior elasyc limit SuperplasYcity at high T Good soc magneyc properyes ApplicaYons: ThermoplasYc forming of metals à processing like plasyc Sports equipment Sensors/actuators Biomedical implants/tools Electronic casings Industrial coayngs Fe- based bulk metallic glasses à Low cost BMG composites w/ crystalline precipitates à Tensile ducylity CommercializaYon of BMGs

5 PredicYon of Fe- based glass forming composiyons 1. Varying atomic radii 2. NegaYve mixing enthalpy between atoms 3. Maximize elasyc strain in matrix Chemical Short Range Order (CSRO) Based on thermodynamic interacyons Predicts cluster formayon 4. ComposiYon near deep eutecycs High interacyon betweens atoms in a cluster Lidle interacyon between clusters à Higher ordered alloys increase GFA Alpha parameter α = n i=1 T l x i T i X i = at % of ith element T i = melting T of ith element T l = liquidus T of alloy

6 OpYmizing the alloy composiyon MatLab program developed by Vecchio et al. [1] à Algorithm to find new composiyons with opymal GFA Combines atomic structural opymizayon models & thermodynamic calculayons of highly stable liquid composiyons near deep eutecycs. Current experimental evaluayon range: Fe: at% à Maximize to minimize cost Ni: 0 30 at % Mo: 0 20 at% à Increases elasyc strain B: 2 8 at % à Promotes short range order C: 0 10 at % [1] Vecchio et al., Mat. Sci. and Engr. A, , p. 135.

7 OpYmizing the alloy composiyon

8 BMG Composite Design Step 1: IdenYfy stable glass for matrix candidate CriYcal issue: Monolithic glass inherently very bridle Failure occurs along a single shear band à AddiYon of hard phase inclusions into glassy matrix to impede shear band propagayon Step 2: Create in situ composite with stabilized ducyle 2 nd phase Hofmann, D.C. et al, Nature, , p

9 ComputaYon design of BMG composites Liquidus Temperature Ti Ni β- Ti Glass Forming Region Cu

10 β- Ti Reinforced Amorphous Matrix Composite Ti 51.4 Ni 42.4 Si 3.9 Mo 2.3 (T2) β- Ti dendrite: Ti Ni Si 1-3 Mo 2-4 β- Ti 50 m Glass matrix: Ti Ni Si 8-13 Mo 1-2

11 Metallic glass composite processing Splat quenching Argon atmosphere Chilled copper plate Before Arc melt ingot (20 g) Push- rod to Yp copper weight à amorphous films (t = 1-3 mm) Semi- solid inducyon forging Acer Processing in 2- phase temperature range: glass (molten) precipitate (solid)

12 CONCLUSIONS on DESIGN OF COST EFFECTIVE BULK METALLIC GLASS COMPOSITES 1. High strength, high elasyc limit, good corrosion and wear resistance, and reasonable toughness make BMGs viable for industrial applicayons 2. ComputaYonal design of BMGs can be done in an expedient manner by using nanoscale tailoring of atomic clusters. 3. SolidificaYon modeling using muly- element phase diagrams can be used to design BMG composites that exhibit tensile ducylity.

13 Future Work Summer 2012 internship at JPL/CalTech Mentor: Dr. Douglas Hofmann [Prof. Vecchio s former graduate student] Low temperature gears for next Mars rover Metallic glass solidificayon experiments at ISS Metallic glass mirror assemblies with low CTE

14 Other material science related acyviyes San Diego Regional Science Olympiad different compeyyons: Bodle rockets Moustrap vechicals Food science Keep the Heat (Thermodynamics) Materials Research Society (MRS) UCSD student chapter Guest speakers from the industry Company tours About 3,000 parycipants: Students Teachers (coaches) Event Captains Top 3 teams advance to state compeyyon

15 Thank You Dr. Kenneth Vecchio Dr. Douglas Hofmann (JPL/CalTech) Department Technical Staff: Wayne Neilson (UCSD, NanoE) Sabine Faulhaber (UCSD, NanoE)