MP159 is a cobalt-nickel-chromium multiphase alloy (UNS R30159, AMS 5842) developed by SPS Technologies as a higher-temperature-capable relative of MP35N, intended primarily for aerospace fasteners and springs that must hold extreme strength in demanding turbine-adjacent environments. Cobalt is the largest constituent at roughly 35.7%, followed by nickel at 25.5%, chromium at 19%, iron at 9%, molybdenum at 7%, titanium at 3%, niobium at roughly 0.6%, and aluminum at about 0.2%. Unlike the cast, carbide-strengthened MAR-M family, MP159 is a wrought alloy that gets its exceptional strength from a combination of multiphase solid-solution chemistry and mechanical processing rather than from a hard carbide network.

MP159's defining characteristic is its processing route: the alloy is cold-worked (typically 45-50% reduction of area) and then age-hardened at around 663°C (1225°F) for four hours before air cooling. That cold-work-plus-age sequence produces an extraordinary combination of strength and toughness - published data shows ultimate tensile strength around 275 ksi and yield strength around 265 ksi in the fully processed condition - while retaining useful ductility. MP159 is rated for continuous service up to about 593°C (1100°F), with short-term capability higher still, which is what distinguishes it from MP35N in applications with a genuine thermal-exposure requirement.

MP159 presents a different machining challenge than the cast MAR-M cobalt superalloys: instead of an abrasive carbide network embedded in a relatively soft matrix, the difficulty here comes from the alloy's genuinely extreme bulk strength. In the cold-worked-and-aged condition, MP159 reaches roughly 265 ksi yield strength - well above what most nickel or cobalt superalloys deliver even at temperature - which means the cutting edge is engaging a fundamentally harder, tougher workpiece from the first pass, not just one that resists softening at speed.

Work hardening on top of that already-high base strength is aggressive: any rubbing, dwell, or inconsistent chip load drives the surface hardness up further and can turn a manageable cut into a rapid tool-failure event. The multiphase cobalt-nickel matrix, strengthened by titanium and niobium-bearing precipitates, also retains strength well into elevated temperature, so - as with the cast cobalt grades - there is little practical benefit to running faster in hopes the material will soften ahead of the tool.

Given MP159's cold-work-plus-age strengthening route, machining should be even more conservative than for as-cast or solid-solution cobalt superalloys of similar composition: low, steady cutting speeds, sharp positive-rake ground carbide or CBN tooling, maximum rigidity with minimal overhang, and continuous coolant to control heat buildup from the material's high cutting forces. Frequent, proactive tool-wear checks are essential, since edge breakdown on a fully aged, high-strength alloy like this can progress very quickly once initiated.