ADVANCED MATERIALS & PROCESSES | SEPTEMBER 2026 36 envelope without assembly steps that introduce joints and tolerance stack-up. Billet machining produces rigid clips and staples, but not internal channels or lattice structures. In each case, the process preserves the alloy while limiting the achievable geometry. TWO APPLICATION FIELDS WITHIN REACH Delivery systems and minimally invasive instruments form the first field. Their function is mechanical: Devices must be advanced, articulated, deployed, retracted, and released through access channels of a few millimeters. The NiTi elements of such systems are conventionally produced as wires, coils, and laser-cut tube segments, then joined to machined components by welding, crimping, or adhesive bonding. Each joint adds tolerance stack-up, an interface that can fail under cyclic load, and an assembly operation at millimeter scale. An additive route allows these functions to be consolidated: a grasper jaw with an integral flexure hinge, a locking clip with a built-in spring element, a steerable tip whose stiffness varies along its length by geometry rather than by joined segments. The same consolidation applies to handle-side components, where superelastic elements provide constant-force response or tactile feedback, and to micro-actuators in general engineering, where a NiTi element and its mounting features can form one part. Orthopedic and bone-contacting applications form the second field. Bone-contacting implants benefit from open, interconnected porosity that supports vascular ingrowth and biological fixation; titanium lattice implants based on this principle are established in spinal surgery. NiTi extends the concept by combining porous architecture with superelasticity, allowing an implant to approach the stiffness of cortical bone while sustaining recoverable deformation under cyclic loading. Patient-specific geometry is the second orthopedic requirement conventional forms cannot address: Implants for craniomaxillofacial and orbital reconstruction derive their surfaces directly from CT or MRI data, and an additive process reproduces this anatomy without dedicated tooling. Staples and compression devices, an established NiTi product category in foot and ankle surgery, indicate a further direction, since fixation geometry, compression elements, and insertion features can be integrated into one part rather than assembled. The two fields differ in their regulatory position, and the difference matters for sequencing. Instruments and delivery-system components are not governed by the implant chemistry limits of ASTM F2063; their requirements are dimensional accuracy, fatigue-relevant surface quality, and a correctly placed transformation window. Bone- contacting implants carry the full implant requirements and therefore define a development target rather than a present offering. The near-term path runs through the instrument: The same process that today produces a FEATURE delivery mechanism establishes the design methods and process controls that implant applications will later require. MATERIALS DATA FOR LMM-PROCESSED NiTi The relevant criterion for any new route is whether it preserves the functional behavior of NiTi. In the development work summarized here, the sinter route retains the Ni:Ti ratio of the starting powder, since no melting occurs, and achieves high density: 98.6% for a coarse powder (<45 µm) and 99.7% for a fine powder (<15 µm)[5]. In the as-sintered condition, the material is functional but not optimized; a fine-powder batch exhibited an Af of approximately 50°C with about 3% retained strain, consistent with the irregular microstructure produced by slow furnace cooling. Heat treatment, applied as for conventional NiTi, is the determining step. Across three heat-treatment conditions, Af decreased from 42.2°C to 8.3°C, placing the transformation below body temperature, while ultimate tensile strength rose from 1259 MPa to 1379 MPa (Figs. 2 and 3). The condition with Af = 8.3°C reached an upper plateau stress of 909 MPa and a lower plateau stress of 487 MPa, exceeding the reference values of ASTM F2516-22 (1070 MPa ultimate strength, 650 MPa upper plateau, 366 MPa lower plateau) in every mechanical criterion while meeting the Af aim[4]. Retained strain after unloading fell below 1%, and elongation at fracture increased with heat-treatment temperature. The functional response of sintered NiTi can therefore be established by the same metallurgical means used for conventional material. The open development item is interstitial chemistry. Carbon introduced by the binder and oxygen absorbed during thermal processing remain above the F2063 wrought- material limits; current sintered values are approximately 0.11-0.18 wt% carbon and 0.18-0.37 wt% oxygen. Fig. 2 — Differential scanning calorimetry of heat treated LMM NiTi (Samples 1-3), heating and cooling at 10 K/min, showing the decrease of Af from 42.2°C to 8.3°C with increasing heat treatment temperature.
RkJQdWJsaXNoZXIy MTYyMzk3NQ==