Authors: Silvia Gaiani, Boštjan Juriševi č, Paolo Veronesi, Igor … · 1)Use our consolidated experience and technical knowledge in titanium alloys transformation 2)Have the possibility

TITANIUM 2009Waikoloa, Hawaii

13 -16 September 2009

CHARACTERIZATION OF TITANIUM ALLOYS CASTED FROM RECYCLED MATERIALSAuthors: Silvia Gaiani, Boštjan Juriševič, Paolo Veronesi, Igor Akrapovič



WHY ESTABILISH A CASTING FACILITIES IN THE COMPANY?

1)Use our consolidated experience andtechnical knowledge in titanium alloystransformation

2)Have the possibility to use recycled titaniumalloys coming from other production processes

3)Produce components with dedicated shapewith a minimum achievable thickness down to1 mm

4)Obtaining parts with good tolerances, reducedmaching time and appreciable surfacefinishing

5)Expand our business in different types ofmarket segments than automotive (medicals,sports goods, arts, entertainment ...)


13 -16 September 2009TYPICAL PHASES OF INVESTMENT CASTING

1. Wax injection for creating positive model2. Waxes assembly on appropriate tool3. Slurry and ceramic shell preparation4. Dewaxing5. Melting in centrifugal vacuum oven6. Shell’s breaking7. Finishing of the parts



AN EXAMPLE OF THE PROCESS -WAX PATTERN PREPARATION

Aluminium tool for wax injection

Wax pattern assembly



Assembly patterns on tree Ceramic shell creation Shell breaking after casting

Casted tree before ball blasting Casted tree after ball blasting

SHELL CREATION AND CASTING


13 -16 September 2009 FINISHED PART



WHICH IS OUR STARTING RAW MATERIAL FOR CASTING?

In our vacuum oven we can melt the following materials:- Titanium alloys, nichel based alloys or superalloys of everyquality, according to EN or ASTM standards requirements- Recycled titanium alloys originated form our productionprocesses, like tube manufacturing, bending, deep drawing, ....



In case of using recycled materials, the different footages are submitted to the following preparation cycle:1. Selection of alloys quality using XRD gun2. Shreding3. Degreasing / Cleaning in alkaline bath4. Drying5. Bricketing

RECYCLING TITANIUM ALLOYS



CHARACTERIZATION OF RECYCLED TITANIUM ALLOYS

Our main quantity of technical scrap owns to the following quality:- Grade 37 (Kobe Steel)- Timetal XT (Timet)- Grade 2 (Nippon Steel)

Using the material mentioned above, we create some specific blend alloys which have been tested in order to obtain a complete characterization.


13 -16 September 2009CHEMICAL COMPOSITION

Every single alloying element plays asignificant role in determinating finalflowability of the material


13 -16 September 2009 GAS CONTENT EVALUATION

The content of gases in titanium alloys is extremely important,because the resistance and ductility of the material issignificantly modified by these elements, especially oxygen.


13 -16 September 2009MECHANICAL CHARACTERIZATION

- TENSILE PROPERTIES -

While Rp and Rm values of the blends are intermediatebetween the base components, their elongation resultssignificantly higher, especially when grade 2 titanium isadded.


13 -16 September 2009MECHANICAL CHARACTERIZATION

- HARDNESS BRINELL-

Results of Brinell hardness test confirm theproperties of the alloys obtained performingtensile test



OXYDATION RESISTANCE TEST(performed in Modena University, Italy)

Prismatic specimens, cast with different blend alloys, have been tested in difference surface finisheng conditions: - As casted (C)- Shot peened (P)- Machined by milling (M)

Duration of tests in the oven (in still air) have been 100 hours at three different levels of temperature:700 °C, 800 °C, 900 °C.



SEM/EDS INSPECTION(performed in Modena University, Italy)

The examination using electronic microscope has been donewith the following targets:- Inspecting morphology and type of oxide which are generatedat different temperature- Studying the influence of surface finishing on castedcomponent- Investigating the thermal resistance of different types ofblended alloys, understanding the role played by single alloyingelements



0XIDATION TESTS @ 700 °C

At 700°C the oxidation on the samplesafter 100 hours is still moderate(around 0,1% in weight)

Anyway, the morphology ofoxide is significantly different,especially depending on thesurface finishing

700 °C – AK 70-30 As Casted (C)

700 °C – AK 70-30 Machined(M)


13 -16 September 20090XIDATION TESTS @ 800 °C

At 800°C the oxidation on thesamples after 100 hours start to bemore visible (around 0,3% in weight)

800 °C – AK 50-50 As casted (C)

800 °C – Pure XT As casted (C)

At this temperature, also adifference in behavior betweenalloys in clearly noticeable



0XIDATION TESTS @ 900 °C

EDS analysis showed that, in the Al-richer samples surface, there is theformation of “spongy” crystallineaggregates containing alumina,surrounded by TiO2 prismatic crystals

At 900 °C the different oxidation resistancebetween the five blended alloys is evident.All the single alloying elements Al, Si andFe play a strategic role

900 °C – Pure G37 As casted (C)

900 °C – Pure XT As casted (C)


13 -16 September 2009INFLUENCE OF OXYGEN CONTENT

Every time that titanium is cast (also if in vacuum oven) anincrease in oxygen content is detected. It is well known thattitanium α alloys are significantly hardened by the interstitialelement oxygen.Example:

Commercially pure titanium alloys Grade 2 and Grade 4 are dissimilar only for the different content of oxygen; in the table above the different mechanical properties are clearly visible (data from ASTM B 365)


13 -16 September 2009RECYCLED MATERIAL 100% FIRST MELT

- Low O2 content (∼0,12%)- Rp and Rm values similar to rolled material- Very high elongation


13 -16 September 2009RECYCLED MATERIAL 100% REMELTED

- Double O2 content (∼0,25%)- Rp and Rm raise approximatly 250 MPa- Elongation reduced to half


13 -16 September 2009CONCLUSIONS

After the series of tests performed on titanium alloys obtainedmixing different recycled materials, we can affirm the following:

- A proper blend of recycled alloys allow tailoring mechanicalproperties (Rp, Rm and elongation) according to the projectrequirements

- The oxidation resistance is particularly good until 850 °C ofcontinuous use; new blends are actually under study to increasethis specific properties

- Blended alloys obtained from recycled materials allow asignificant cost reduction


13 -16 September 2009EXAMPLES OF APPLICATIONS

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Authors: Silvia Gaiani, Boštjan Juriševi č, Paolo Veronesi, Igor … · 1)Use our consolidated experience and technical knowledge in titanium alloys transformation 2)Have the possibility