Induced Positron Analysis (IPA)

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Overview
Proprietary methods identify damage in metal alloys prior to crack formation

The Induced Positron Analysis (IPA) nondestructive inspection capabilities are currently being developed and commercialized by Positron Systems. These methods, based on positron annihilation principles, are sensitive to variation in material microstructure at the atomic scale. This enables a highly sensitive means for many practical NDT applications of metal alloy condition such as cold working, heat treatment, operational damage, and manufacturing process effects, including differentiating the microstructure variations associated with phase changes.

IPA highlights Include:
- Sensitive probes measure material defects in microstructure (10-9 to 10-6m scale)
- Proprietary NDE methods based on positron annihilation spectroscopy
- Unique NDE method identifies damage in metal alloys prior to crack formation
- Proven Sensitivity to measure:

 

Plastic Strain

Surface Coatings

Creep

 

Case Hardening

Annealing

Engineered Residual Stresses

 

Embrittlement

Fatigue

 

 

IPA Process
General methods used for induced positron analysis

IPA Process

IPA inspection involves two processes. Positrons are first induced in the material to be tested. As they diffuse through the material, they interact in defect regions, if they exist, in the crystalline structure by an annihilation event with electrons in vacancies, voids, dislocations, and other defects. The second part of the inspection process is detection of the annihilation activity. Gamma radiation spectroscopy is used to measure the proportion of these atomic level defects in the probed material. IPA is used to measure material condition within a region of material beneath the surface. To generate positrons in the inspected material, source probes are placed on the surface of the material to be inspected. A schematic of the positron implantation process is shown below. An IPA measurement involves hundreds of thousands of these events.

 

Positron Annihilation
Basic process of positron annihilation and how this is an idicator of lattice defects

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The physical phenomenon being measured in positron annihilation is briefly described as follows: positrons diffusing through a material are repelled by the positively charged protons in atomic nuclei. Positrons tend to trap in regions where atomic nuclei are further spaced, such as the mono vacancy shown below. Positron-electron annihilation in areas away from atomic nuclei tends to be with valence electrons, which travel at lower velocities. Annihilation events in areas free from lattice defects have a greater probability of occurring with core electrons, which have higher velocities. The velocities of the electron in each annihilation event influence the Doppler broadening of the 511 keV peak, the energy level produced during each of the positron-electron annihilation events.

Doppler broadening measures the gamma ray energy distribution centered at 511 keV and is influenced by concentrations of lattice structure defects. Fewer defects mean more annihilation events occur with the higher velocity core electrons, and produce a wider 511 keV peak as shown below. This response is quantified using the "line shape" parameter or "S" Parameter.

 

Inspection Manager
Application software developed by Positron Systems designed with flexibility in mind

Inspection Manager

The IPA data acquisition and processing are performed using the Inspection Manager application software and PS6100 automation platform, both developed by Positron Systems. Inspection Manager allows for organization and analysis of data specific to materials and tested conditions into a SQL database. The software was designed with flexibility in mind, and is therefore used for all internal R&D testing as well as by trained NDE technicians performing tests developed specifically for customer application. The browser based user interface is shown below. The database can be accessed remotely for data analysis or monitoring of automated tests via a simple secure internet connection.

 

PS6100
Positron Systems PS6100 IPA measruement system

PS6100 Console

The PS6100 IPA measurement system, shown above, enables fully automated measurements of a sample. Each acquisition performed on a part, including component setup and positioning, data acquisition, and post-processing, is completely controlled by the system to ensure accurate and repeatable IPA measurement data.

All of the required equipment to perform IPA-S measurements is contained within the cabinet. The system only requires facility 120 V AC power, an internet connection, and compressed air to support full functionality.
The part manipulator and gamma radiation detector are shown below. The PS6100 is capable of four axes of movement- x, y, z, and theta. The manipulator can move a part of up to 15 kg maximum 1000 mm in the X direction and 600 mm in Y. The radiation detector can extend 300 mm above the table on the Z axis stage. The pneumatically actuated part gripper can rotate 360 degrees. Therefore, both complex part geometries and parts of substantial size (600 mm maximum dimension) can be inspected on the platform.