ED0371037revE_Nb_Technical_Requirements_Josh_Christopher Edwards.pdf

TECHNICAL SPECIFICATIONS FOR HIGH RRR GRADE NIOBIUM SHEET FOR

USE IN SUPERCONDUCTING RADIO FREQUENCY CAVITIES

ED0371037.RevE

TECHNICAL SPECIFICATIONS FOR HIGH RRR GRADE

NIOBIUM SHEET FOR USE IN SUPERCONDUCTING

RADIO FREQUENCY CAVITIES

Fermilab Specification: ED0371037 Rev E

Revision ER/ECO Date Description Originated By Approved By

ER

#8493 09Aug2006 Original Issue

P. Bauer, C Antoine

M. Ross

A

ECO

#8736 09Jul2007

Changed RRR Requirement from 250 to 300

L. Cooley M. Champion

B

ECO

#10250 08Dec2011

Modifications in response to procurement history

L. Cooley M. Champion

C N/A 27Aug2013 Modifications in response to procurement history L. Cooley M. Foley

D N/A 27Jul2018 Modifications in response to flux expulsion behavior

S. Posen, M. Martinello, S. Chandrasekaran A. Romanenko

E N/A 06Mar2020 Added the minimal acceptance and desired acceptance for PIP-II S. Chandrasekaran G Wu

Fermi National Accelerator Laboratory Applied Physics & Superconducting Technology Division

SRF Measurements & Research Department P.O. Box 500 - Batavia, Illinois - 60510

1.0 GENERAL

Fermi National Accelerator Laboratory (FNAL, Fermilab) designs and constructs superconducting particle accelerators. This specification addresses superconducting radio-frequency (SRF) cavities, which are a key component of particle accelerators. Performance of these cavities depends on high purity, high RRR, annealed niobium due to its superior superconducting properties. Maintenance of high purity is of utmost concern throughout all steps, since this is the single most important factor affecting end performance. Components are fabricated from plate and rod stock by machining, deep drawing, or other metal-forming processes, for which ductility and formability are important.

Components are joined by electron-beam welding to maintain high purity. The RF cavities are tuned to a very precise frequency, and to maintain this tune suitable mechanical strength and tight material tolerances must be maintained. Cavities are operated in a cryogenic vacuum environment, requiring pressure certifications and material traceability. All of these factors motivate the content of this specification.

Of special note, this specification seeks material of a premium grade, for cavities intended to meet performance requirements for the PIP-II Project. Specifications catering to ILC gradient requirements were captured in Rev D of this document.

2.0 APPLICABLE DOCUMENTS

2.1 Applicability

The following documents, of issue in effect on date of invitation for bids, request for bids, or request for proposal, form a part of this specification to the extent specified herein:

ASTM B-391 Niobium and Niobium Ingot Alloys ASTM B-393 Standard Specification for Niobium and Niobium Alloy Strip, Sheet, Foil and Plate ASTM E-3 Standard Guide for Preparation of Metallographic Specimens ASTM E-8 Method of tension testing of metallic materials.

ASTM E-112 Standard method for determining the average grain size ASTM E-883 Standard Guide for Reflected–Light Photomicrography ASTM E2627 Standard Practice for Determining Average Grain Size Using Electron

Backscatter Diffraction (EBSD) in Fully Recrystallized Polycrystalline Materials

ASTM E384 Standard Test Method for Knoop and Vickers Hardness of Materials FNAL ED0371109 Test Method for determining residual resistivity ratio (RRR) of cavity-grade niobium FNAL ED0464049 Procedure for handling and inspection of incoming niobium sheets used for SRF cavities

2.2 Source of Documents

The documents may be obtained from the following sources:

ASTM Documents:

American Society of Testing and Materials

Fermilab Technical Division Quality and Materials Department

1916 Race Street Philadelphia, PA 19103

P.O. Box 500, M.S. 316 Batavia, IL 60510

3.0 DEFINITIONS AND TERMINOLOGY

Lot — The definition used in ASTM B393, “a lot shall consist of all material produced from the same ingot at one time, with the same cross section, processed with the same nominal metallurgical parameters and heat treated at the same conditions”, is modified herein to accommodate differences between the capacity of annealing furnaces used for heat treatment and the quantity of sheets produced from a single ingot. For the purposes of this specification, a lot shall consist of all material produced from the same ingot at one time, with the same cross section, processed with the same nominal metallurgical parameters, and heat treated under reproducible conditions.

Heat treatment batch — A heat treatment batch shall consist of all material placed into an annealing furnace at one time, for which particular parameters of the heat-up, soak, cool-down, atmosphere, and other details apply to the entirety of material.

Notes: (1) A large lot may be sub-divided into several heat treatment batches if the furnace capacity is smaller than the lot size. (2) Multiple small lots may be collected in a single heat treatment batch for furnaces with large capacity.

Transverse — Orientations described as transverse shall be the direction perpendicular to the primary rolling direction and perpendicular to the thickness of the sheet.

Transverse cross-section — The transverse cross-section shall contain the transverse orientation, i.e. it is the planar cross-section perpendicular to the rolling direction.

Longitudinal — Orientations described as longitudinal shall be the direction parallel to the primary rolling direction.

Longitudinal cross-section — The longitudinal cross-section shall be the plane defined by the rolling direction and the sheet thickness.

4.0 REQUIREMENTS

4.1 Materials and Chemical Composition

The chemical composition shall conform to ASTM B393, Type 5, RRR grade niobium.

Manufacturer shall note that the ingot chemistry and finished product chemistry is closely related to the value of residual resistivity ratio RRR.

4.2 Manufacture

Manufacture shall conform to the stipulations contained in ASTM B393, with the additional provision that manufacturer may include grinding and pickling in the manufacturing technique, provided that other requirements for surface quality and chemical composition are met.

Manufacturer shall strive whenever possible to use tooling and equipment dedicated to the manufacture of niobium, tantalum, titanium, zirconium, or their alloys. Manufacturer shall note that rolling mills used to produce iron or steel may embed magnetic particles into sheets, which are particularly harmful for the final application. Multiple QC tests and other analyses will be used to screen for such defects. Presence of magnetic materials may cause rejection of the sheet lot.

4.3 Dimensions and weight

Dimensional tolerances stipulated in ASTM B393 shall generally apply to width and length.

Sheets manufactured for SRF cavity half cells shall conform to applicable sheet drawing(s) for thickness tolerance. Flatness of 6% shall be required; this relaxes the specification for RRR grade sheet stipulated in section 9.2 of ASTM B393.

4.4 Mechanical requirements

The final product shall conform to the mechanical properties at room temperature given in Table 2, defined as per ASTM E-8 and E-384. Where applicable, values given by this specification supersede or add to the requirements of ASTM B393 Annex A1.

Manufacturer shall note that any mechanical anisotropy may be amplified by the intrinsic mechanical anisotropy of niobium itself, i.e. up to a factor of 2 for some properties. Residual texture could produce poor forming and polishing characteristics.

Table 2. Mechanical property specifications

Property Value

ASTM B393 Minimum Acceptance Desired Acceptance Yield Strength (0.2% offset)

50 MPa (7,200 psi) min No max

50 MPa (7200 psi) min 95 MPa (14,000 psi) max

Ultimate tensile strength 95 MPa (14,000 psi) min 95 MPa (14,000 psi) min 175 MPa (26,000 psi) max

Elongation in 25.4 mm (1- inch) gauge length

30% min 30% longitudinal min 30% transverse min

50% longitudinal min 50% transverse min

Strain hardening coefficient (informative)

-- -- 0.3

Hardness Average < 60 HV10 Average < 60 HV10

Average < 50 HV10

4.5 Grain size and microstructure

Sheets shall be delivered in a minimum 95% recrystallized state. This supersedes any of the ASTM specifications. Grain aspect ratio longitudinal with and transverse to the rolling direction shall not exceed 2.

The minimal acceptance criteria of sheets shall have sheet grain size between ASTM #4 and #6.

The desired average grain size of sheets shall be ASTM #5 (63 µm), with local areas no larger than ASTM #4 and no smaller than ASTM #6.

See section 5.4 for testing methods to measure grain size and aspect ratio.

4.6 Electrical requirements

The final product shall have a measured Residual Resistivity Ratio (RRR) value greater than 300 as defined by FNAL ED0371109. This may be an average value among all test specimens for a given lot. If an average value is reported, the coefficient of variation of RRR values shall not exceed 10% of the average value, and no single measured value shall be less than 270. This requirement supersedes ASTM B393 for Type 5 niobium.

Manufacturer shall note that FNAL ED0371109 defines RRR on the basis of room temperature (298 K) to be consistent with other international standards, whereas ASTM B393 defines RRR on the basis of ice point (273 K). The variation of RRR with temperature between 273 K and 298 K is approximately 10%, i.e. the requirement of RRR = 260 in ASTM B393 will produce and equivalent value of RRR = 286 under the FNAL standard.

4.7 Quality and Finish

The material shall be delivered with bright surface finish such as that produced by pickling or light etching. Compliance with stipulations of ASTM B393 Annex A1 on surface finish shall be maintained. The surface shall be free of oxide inclusions, cracks, blisters, folds, or laminations.

The delivered material shall be free of injurious imperfections of a nature that would interfere in the forming operation including, but not limited to, orange peeling, dislocation pitting, and etch pits. Manufacturer may remove surface imperfections provided other requirements of this specification are retained after the removal. Particular care should be taken in the final handling of the soft, recrystallized metal to avoid marring, indentation, and the inclusion and imbedding of particles of foreign material in the surface of the sheets.

Inspection for such defects is described in section 8.0.

5.0 TESTING

The tests listed below are the minimum required and may be in addition to any controls, examinations, inspections, or tests normally employed by the seller to assure the quality of the product.

5.1 Chemical composition

Manufacturer shall supply a test report certifying the values of ingot chemistry. A certification shall be supplied for each lot if more than one lot is used to complete the sheet order.

Manufacturer shall supply a test report certifying the values of the interstitial elements C, O, N, H in the final product for each heat treatment batch. Enough samples shall be acquired to ensure that results are representative of the entire batch.

In both cases, stated values shall be an average over the test specimens. Manufacturer shall state the test technique used to determine these values, along with information describing the sensitivity of the test method for the elements in question. Manufacturer shall provide the uncertainty based on the number of samples tested and the systematic and random uncertainties in the test method.

5.2 Samples for property testing

Property tests shall be conducted and reported for the final product. Sampling shall conform to ASTM B393 section 11.

Manufacturer shall determine the number of combinations of sheet lots and heat treatment batches used to produce the final product. For example, suppose a large lot A is combined with a small lot B to meet an order, and suppose that for reasons of furnace capacity a heat treatment batch 1 cannot accommodate all of lot A, so that the remainder of lot A is combined with the entire lot B to form heat treatment batch 2. Samples would therefore be required from A1, A2, and B2.

A minimum of two sheets, chosen at random and to be representative of the finished product, shall be set aside as samples for each combination of lot and heat treatment batch. This requirement supersedes ASTM B393 section 12. For each combination, one of the samples shall be sent to FNAL for measurements and acceptance. The other samples shall be subdivided into test specimens for each of the tests below under arrangements made by the manufacturer. Cutting procedures shall not result in a residue on the test specimen or produce any artifact in properties.

Test specimens shall not be taken near any product marking.

5.3 Residual Resistivity Ratio (RRR)

RRR shall be measured for at least one specimen from each sample according to Fermilab

ED0371109.

If the RRR measurement cannot be completed per 5500-ES-371109, vendor may arrange for an alternative test method, provided that such method is calibrated by samples measured according to ED0371109. FNAL can provide these samples. Manufacturer shall note that measurements of residual resistance performed in magnetic field can suffer large errors introduced by non-linear magneto-resistance.

5.4 Microstructure

Microstructure analyses shall be reported for each sample. Manufacturer shall obtain photomicrographs per ASTM E-3 and E-883. Micrographs shall be obtained for specimens of transverse and longitudinal cross-sections. One representative photomicrograph at x500 magnification per specimen orientation (longitudinal and transverse) and one representative photomicrograph at x50 magnification per specimen orientation shall be delivered per sample.

ASTM E-112 shall govern reporting of microstructure measurements. The grain size shall be measured and value shall be reported as an average taken among test specimens with same orientation for each sample. The fraction of recrystallization shall also be reported as an average among test specimens with same orientation for each sample. Manufacturer shall, in addition, report aspect ratio to assure compliance with requirement 4.4.

5.5 Mechanical properties

Mechanical properties shall be reported for each sample to verify compliance with requirements.

Mechanical measurements shall be performed on tensile specimens in accordance with ASTM E-8. Test specimens shall consist of longitudinal and transverse orientations. For the tensile measurement, the rate of strain shall not exceed 0.010 inch/inch-minute through the 0.2% offset yield strength. The rate-of-strain may be increased to not more than 0.05 inch/inch-minute thereafter. Compliance with ASTM B393 will meet this strain rate requirement.

Hardness measurements shall be reported for ingot as well as for each sample of the final product.

ASTM E-384 (which replaces E-92) shall govern hardness measurements. Measurements may be conducted on separate test specimens, or may be incorporated with the same test specimens used for other tests. For final product, hardness testing shall be performed on both the transverse and the longitudinal cross sections. Microhardness is an acceptable substitute for macrohardness when information on the cross sections is provided.

6.0 PRODUCT MARKING

Manufacturer shall permanently inscribe a symbol identifying the manufacturer, the lot number, the heat treatment batch number, the primary rolling direction, and a unique sequential number onto each sheet. Fermilab will produce circular pieces with diameter equal to the entire length or entire width from the sheets. The marking shall be consistently placed in a corner of the sheet in such a way that this central circular region is not affected in any way by the marking.

Manufacturer shall strive to coordinate sheet numbering with sequential location along the lot during its final rolling, and/or to the location of sheet in the furnace. This optional record shall assist both Fermilab and the manufacturer in improving the sheet product.

7.0 PACKAGING

Sheets shall be prepared for shipment in accordance with commercial practice and in compliance with applicable rules and regulation pertaining to the handling, packaging, and transportation of the product to ensure carrier acceptance and safe delivery. Each sheet shall be individually wrapped with non-abrasive, anti-tarnish paper. When sheets are stacked, packing material shall prevent wrapped sheets from sliding against each other. Separating sheets by supporting the corners or placement of fresh polycarbonate foam between sheets are recommended methods of packing when sheets are not too large. Manufacturer shall note that some fabrication processes remove the center of sheets, and it may therefore be possible to support the sheet at the center, as well as the corners, to prevent sagging during shipment to Fermilab. Sheets that are especially large, in particular those with any dimension longer than 60 cm (24 in), may have insufficient strength to prevent plastic deformation and warping when not supported adequately. It is recommended that the vendor confer with Fermilab prior to shipping large sheets.

Wooden containers that prevent impact damage and bending shall be used. The containers shall be constructed such that they can be handled by forklift. Sharp fasteners that penetrate the container, such as nails or screws, shall be avoided if possible, and in any event provisions shall be made that inadvertent penetration of points cannot come into contact with the sheets.

Banding shall be applied in such a way that the bands must be removed if the container is opened.

A marking shall be applied to the bands that identifies the manufacturer or manufacturer’s shipping agent, so as to indicate if the bands may have been replaced (e.g. as a result of customs inspection).

No palletized load shall exceed 1,000 kg (2,200 pounds). The buyer reserves the right to inspect the packaging prior to shipment.

8.0 VISUAL INSPECTION

Both the manufacturer and Fermilab shall visually inspect the product. Inspection shall use standard laboratory illumination. Inspecting agents may have vision corrected to 20/20 but shall complete the inspection without additional magnifying aids. Inspection shall be conducted from a typical distance of 1 foot (30 cm) from the surface.

Under these conditions, obvious gouges, deep scratches, orange peeling, and other features shall be noted based on sheet number and location. Fermilab will measure the depth of surface flaws with a Taylor-Hobson profilometer. Fermilab ED0464049 explains the criteria for visual inspection that may produce rejection of any sheet or the entire sheet lot.

9.0 QUALITY ASSURANCE

The manufacturer shall maintain a documented quality assurance program that will insure that each item offered for acceptance or approval conforms to the requirements herein. A Quality Assurance plan must be submitted with the proposal and must be approved prior to the award of the contract.

Fermilab reserves the right to have its technical or procurement representatives witness manufacturing steps, tests and inspections established under the seller's quality assurance program to demonstrate compliance with the specifications. Any information of a proprietary nature must be identified in the bid process.

Documentation shall be supplied prior to any shipment of sheets. Documentation shall include:

Manufacturer’s lot number Manufacturer’s heat treatment batch number Manufacturer’s product description Manufacturer’s fabrication or shipment date Fermilab PO number Paper or electronic records of all tests and inspections

10.0 ACCEPTANCE

FNAL reserves the right to perform additional tests and inspections on the delivered material to verify compliance with the requirements herein. If the results of these tests show that the delivered material is not in compliance with sections 4.0 and 5.0 of this specification, the material will be submitted to a third party testing laboratory which is acceptable to both FNAL and the vendor. Costs for such tests shall be shared between FNAL and the vendor. If portions of the material are still not acceptable to FNAL after this assessment, the vendor is obligated to provide replacement material or agree on a re-work of the material with FNAL.