# Presentation: 473542

## Cavities from Ingot with Large Grains

- W. Singer

- W. Singer

## Possible advantages:

-  Seems to be cost effective
-  Predictable spring back for deep drawing
-  Better purity. RRR=600 in the ingot is achievable
-  Simplified quality control (reduced number of measurements: grain size etc, possibly no scanning)
-  Simplified treatment: possibly BCP instead of EP

- Steps of conventional sheet fabrication

- Disc for half cell

- Discs from large grain ingot

- Large grain ingot. Diameter of 280-300mm

- Cut off

- W. Singer

## Task: starting with cm size grain of ingot finish with ca. 50 μm uniform grain on the sheet without contamination of Nb on the chain of steps

- Recrystallized niobium sheet

- Rolled Nb sheet before final annealing

- Ingot

- After hammering

- Rolled rough plate

**Microstructure of Nb on different stages of sheet production**

- Standard ingot has already cm size grain. How to increase the grain with the aim: single crystal (large grain)??

- W. Singer

## Large silicon single crystal

- Is it possible produce single crystal Nb ingot of the diameter 265 mm for TESLA shape cavity???

- Applying of special methods for single crystal growing (Czochralski, Zone melting)

- W. Singer

## Disc from HERAEUS ingot produced by special melting parameters

-   Slow cool down
-  Play with electron beam pattern

- 265 mm

- W. Singer

## W. Singer

## Specific behavior of the discs from large grain Nb ingot have to be understood: 

- Strain-stress curves of Nb after annealing

- Grain size versus annealing temperature

- Strain-stress curves of large grain Nb (Heraeus)

- Specific behavior of the discs from large grain Nb ingot have to be understood:
-  High elongation at break
-  Grain boundaries
-  Texture

- W. Singer

## Eddy current scanning image of the Nb disc from HERAUS ingot. Steps on grain boundaries

- W. Singer

## Grain Boundary BCP 1:1:2

**Grain Boundary BCP 1:1:2**

- Grain boundary width after 10μm BCP

- Grain boundary width after 150μm BCP

- Grain boundary depth and width in μm versus thickness of removed layer

- Surface profile measurement after 100μm BCP (right). The surface of the grain itself is very smooth.
-  Profile peak height and valley on grain boundary can be seen.

- W. Singer

## One large crystal

- Grain boundary between two large crystals

- It seems that no new grains appear in the EB welding area.

- W. Singer

## The crystal lattice in neighboring grains is the same but has a different orientation (left). Example of Nb microstructure (right)

- The anisotropic properties of a material is the average of anisotropic properties of its crystallites

- W. Singer

## Texture measurements (BW5, HASYLAB)

- W. Singer

## Principle of Bragg reflection

- Millers atomic planes

- Two representations of an crystal orientation:
- “metallurgical” (hkl) [uvw]
-  by the Euler angles

- W. Singer

## Stereographic projection

- Pole figure

- Powder

- Disc of conventional Nb ingot

- Cubic crystal

- W. Singer

## HERAEUS

- Pos 11 green (grün)
- Pos 12 dark blue (dunkelblau)
- Pos 13 red (rot)
- Pos 14  light blue (hellblau)
- Pos 10 orange (orange)

- HG Brokmeier
- TEXMAT

- Representation of the cube orientation in the stereographic projection for the central crystal. Reflexes of typical single crystal observed

- The 100 pole figure shows an ideal cube position of 18° rotated and 5° tilted

- W. Singer

## HERAEUS

- Pos 6 yellow (gelb)
- Pos 7 light gray (hellgrau)
- Pos 8 red (rot)
- Pos 9 blue (blau)

- In allen Fällen ist eine (110) annähernd parallel zur Oberfläche

- HG Brokmeier
- TEXMAT

- Representation of the cube orientation in the stereographic projection for the edge crystals

- Edge crystals show a significant change of the orientations in comparison to central crystal. A big scattering of the crystal orientations is observed (100 pole figure)

- Pos. 5 und Pos. 8 are measured within of on edge crystal and shows a small deviation from each other (green and red points)

- W. Singer

## Is it realistic to fabricate cavity for XFEL from ingot discs with large grain??

- 1. How cut discs cost effective keeping the tickness tolerances +/- 0,1 mm and producing smooth surface, keeping the high purity of Nb ?(Electric Discharge Machining EDM applied at JLab seems not to be a solution; costs ca. 800 €/disc)
- 2. Are the mechanical properties good enough for deep drawing of half cells of TESLA shape from discs?

**Is it realistic to fabricate cavity for XFEL from ingot discs with large grain??**

- W. Singer

## Cut discs by wire sawing seems to be cost effective.

- Thickness of Nb discs from Heraeus ingot cut by wire saw (meet thickness tolerances)

- Thickness tolerances seems not to be a problem.

- W. Singer

## Large grain single cell cavities from HERAEUS material (ACCEL fabrication)

- W. Singer

## Planned activities  

- Fabrication and testing of several single cell cavities (TESLA shape) from large grain Nb
- Fabrication and testing of two 9 cell cavities (TESLA shape) from large grain Nb
-  Continue joint efforts with EB melting companies in order to produce ingots with single crystal discs of sufficient dimensions for XFEL cavities
-  Discs cut procedure in order to prevent Nb pollution
-  BCP and EP experiments, especially behavior of grain boundaries
-  Accuracy of the half cell shape from large grain Nb

- W. Singer